Methods of and apparatus for cleaning coal

ABSTRACT

Methods of and apparatus for cleaning coal in which fluorochlorocarbons are used as parting liquids. Various novel techniques, components, and combinations thereof are employed to maximize efficiency; to minimize costs and adverse environmental impacts; to make it possible to recover coal of a character which has heretofore been economically unrecoverable; to produce a superior product; and to reach other worthwhile goals.

This application is a continuation-in-part of application Ser. No.423,577 filed Jan. 14, 1974 (now abandoned).

Our invention relates, in one aspect, to novel, improved techniques forseparating coal from the foreign material with which it is found innature and elsewhere.

Raw or as mined coal commonly contains foreign matter in amounts as highas 20 to 60 percent by weight. Even though the cost of doing so canbecome relatively high ($1.50 to $4.00 per ton for a product selling atup to $60 per ton), coal is in almost all cases cleaned to rid it of theforeign material prior to use because of: environmental factors,economic considerations such as the cost of hauling unusable materialover extended distances, and limitations on the amount of foreignmaterials which can be tolerated in the process in which the coal is tobe used.

Many techniques for cleaning coal have heretofore been proposed; and anumber of these are in current commercial use including air separation,jigging, froth flotation, cycloning, and shaking on Deister tables.

There are disadvantages to each of the foregoing techniques for cleaningcoal. One common to all of them is that only a narrow size consist canbe handled; that is, the coal to be processed must consist of particlesin a relatively narrow size range. This may require that the coal beseparated into two or more fractions before it is cleaned, adding to thecost of cleaning the coal.

Another disadvantage of currently employed cleaning techniques such asjigging and shaking on Deister tables is that they are ofteninefficient. Such techniques take advantage of the relative behavior ofcoal and foreign material in a moving stream of water, and many coalshave specific gravities which make dynamic separation inefficient. Manyof the coal particles will act like and settle into the bed of foreignmaterial rather than migrating to a separate strata.

Also, hydraulic separation techniques require large quantities of water.This is an important disadvantage, especially in arid regions or whereenvironmental requirements demand that the plant water circuit becompletely closed; i.e, that there be no water effluent.

Cyclones are used to only a small extent because of the expense and poorproduct yield.

Froth flotation is another coal separation technique that has fromtime-to-time been touted. However, froth flotation requires a degree ofsophistication in preconditioning and flotation chemistry that is inmost cases not available in the field and the size consists that can behandled are limited. Accordingly, while efficient when properly carriedout, froth flotation is not used to any significant extent.

Another type of coal cleaning process which has been proposed is gravityor sink-float separation. This process takes advantage of thedifferences in specific gravity between coal (typically 1.25 to 1.55)and the foreign material associated therewith (typically 1.8 to 6.0) toseparate the coal.

The coal and foreign matter are introduced into a body of a partingliquid having a specific gravity intermediate that of the coal and theforeign material. By virtue of Archimede's principle, the coal rises tothe top of the parting liquid; and the foreign matter or gangue sinks tothe bottom. The two layers of material, respectively termed "floats" and"sinks", are recovered separately from the parting liquid.

Gravity separation using a moving aqueous slurry of magnetite as theparting liquid is in widespread use today.

Like other currently employed techniques, gravity separation as nowpracticed has significant disadvantages. One is that the coal must be inthe form of relatively large particles (typically 10 inches to 1/4inch).Otherwise, the separating velocities of the coal relative to induced orrandom velocities in the separating vessel will be so small that coalparticles will report to the sinks and particles of foreign materialwill report to the floats.

The requirement that the coal have a minimum particle size on the orderof 1/4 inch also means that, in many cases, considerable amounts ofpyrites may be left in the product coal. In some coals large quantitiesof pyrites exist in particle sizes as small as -200 mesh (this and allsieve sizes referred to hereinafter are of the U.S. Standard series).Therefore, if the coal is only reduced to a 1/4 inch particle size priorto gravity separation, large quantities of pyritic sulfur will remainwith the product coal.

Another important disadvantage of gravity separation as currentlypracticed is that fine coal particles or clays, if not completelyremoved from the plus 1/4 inch coal prior to separation, can foul thebath. This increases the viscosity of the bath, resulting in poorseparation efficiency and magnetite recovery.

The coal product of the magnetite-water separator must be mechanicallyor thermally dried or both. Because water has a relatively high boilingpoint and a high latent heat of vaporization, the cost of drying thecoal can be considerable.

Other gravity separation techniques for cleaning coal are described inU.S. Pat. Nos. 994,950 issued June 13, 1911, to DuPont; 2,150,899 issuedMar. 21, 1939, to Alexander et al; 2,150,917 issued Mar. 21, 1939, toFoulke et al; 2,208,758 issued July 23, 1940, to Foulke et al; 2,842,319issued July 8, 1956, to Reerink et al; 3,026,252 issued Mar. 20, 1962,to Muschenborn et al; 3,098,035 issued July 16, 1963, to Aplan;3,261,559 issued July 19, 1966, to Yavorsky et al; and 3,348,675 issuedOct. 24, 1967, to Tveter. The gravity separation techniques disclosed inthese patents differ from that just discussed primarily in the partingliquids the patentees propose.

Our novel process for cleaning coal is, like those described in thejust-cited patents, of the gravity separation type. However, a farsuperior parting liquid is employed; and, as a result, our processenjoys a number of advantages not possessed by the patented processes.

In particular, we employ as a parting liquid a fluorochloro derivativeof methane or ethane (hereinafter referred to as a "fluorochlorocarbon")or 1,2-difluoroethane.

At least 24 derivatives fitting the foregoing description have beenreported in the literature. Of these, 16 are of no interest becausetheir boiling points are so low that the cleaning process would have tobe refrigerated, which is obviously impractical, or so high that thecost of recovering them from the clean coal and rejects would beprohibitive. In fact compounds in the latter category would be inferiorto water-based parting liquids even though they are much more expensive.

The fluorochlorocarbons which we consider suitable because of theirboiling points (ca. 40°-150° F.) and other physical characteristics (lowviscosity and surface tension and useful specific gravity) and theirchemical inertness toward coal and other materials under the processconditions we employ are:

1-Chloro-2,2,2-trifluoroethane

1,1-Dichloro-2,2,2-trifluoroethane

Dichlorofluoromethane

1-Chloro-2-fluoroethane

1,1,2-Trichloro-1,2,2-trifluoroethane

1,1-Dichloro-1,2,2,2-tetrafluoroethane

Trichlorofluoromethane

Of the listed compounds, all but the last three are at the present timetoo expensive to be practical from an economic viewpoint. And, of thelatter, trichlorofluoromethane is preferred because of its optimumphysical properties, its chemical activity, and its low cost.

Also, this compound has an almost ideal boiling point and an extremelylow latent heat of vaporization (87 BTU/lb as opposed to 1000 BTU/lb forwater). Accordingly, the compound can be recovered from solids withwhich it is associated by evaporation with only a modest expenditure ofenergy.

A principal advantage of our novel process for cleaning coal iseffectiveness.

The efficiency of a coal cleaning operation is generally ascertained bya washability study which, in principle, identifies how closely theoperation comes to processing the coal to a theoretical level ofcleanness. While there is no industry wide standard for performingwashability studies, the procedures all have much in common. The coal tobe rated is sampled, graded into different fractions by size consist,and subjected to gravity separation in a mixture of hydrocarbons andhalogenated hydrocarbons or in an aqueous salt solution for an extendedperiod of time. Characteristics such as yield and moisture, heat value,ash, and sulfur content are then ascertained and reported.

With our novel process, we are consistently able to obtain higher yieldsand lower ash, sulfur, and moisture contents than are indicated to betheoretically possible by many washability study procedures. This isimportant from both the economic and ecological viewpoints.

Parting liquids which resemble ours to the extent that they arehalogenated hydrocarbons have heretofore been disclosed in the Tveterpatent identified above. According to the patentee these parting liquidsare suitable for beneficiating coal.

All of the compounds listed in the Tveter patent contain iodine orbromine or both; as a consequence, they have a number of disadvantages.

One is that their boiling points are too high for the compounds to be ofany practical value in the processing of coal. A substantial amount ofthe parting liquid is chemically adsorbed on the particles of the coaland the gangue in any separation process. Economics dictate that thisparting liquid be efficiently recovered and that the recovery beeffected at low cost.

In our opinion the only practical way to recover the parting liquid atthe present time is to do so in vapor form. The energy required torecover high boiling point compounds by this technique makes their useeconomically impractical. In fact one paper flatly states that directevaporation is "not applicable" to liquids with high boiling points(Tippin et al, Heavy Liquid Recovery Systems in Mineral Beneficiation,SME TRANSACTIONS, March 1968, pp. 15-21).

Even assuming that they would be effective, other techniques forrecovering a halogenated hydrocarbon parting liquid such as washing thefloats and sinks with water and then recovering the parting liquid fromthe wash water (see Baniel et al, Concentration of Silicate Minerals byTetrabromoethane (TBE), SME TRANSACTIONS, June 1963, pp. 146-154) wouldlikewise be economically impractical, especially in circumstances wherethe customer's specification requires that substantial amounts of thewash water subsequently be removed from the coal. The same would be trueof the even more complicated parting liquid recovery scheme usingsolvents described in Patching, Developments in Heavy-Liquid Systems forMineral Processing, MINE & QUARRY ENGINEERING, April 1964, pp. 158-166.

The problems of recovering a parting liquid as disclosed in Tveter arecompounded when the solids, like coal, have microcracks, a large volumeof pores, and other defects into which the parting liquid can beabsorbed. Recovery of such liquid can easily become economicallyimpractical.

Another disadvantage of most of the Tveter compounds is that theirspecific gravities are too high for them to be of much value for coalbeneficiation. Bituminous coals have specific gravities in the range of1.25-1.55 as indicated above, and parting liquids having specificgravities above 1.70 are of little importance as the amount of ganguewhich reports to the floats with the coal becomes too high. All of thecompounds listed by Tveter have specific gravities above 1.70.

Furthermore, a number of the listed compounds are little more thanlaboratory curiosities; they are not commercially available at all.Others, which can be purchased from suppliers of rare chemicals in smallamounts, are too expensive to be of any value. For example, the pricequoted for Tveter's 1,1-dibromo-2,2-difluoroethane is $431 per pound.

Finally the Tveter list includes compounds which are anesthetics(1,2-dibromo-tetrafluoroethane, for example) and narcotics (such astrichloroethylene) and others which have a relative high level ofmammalian toxicity such as carbon tetrachloride.

Halogenated hydrocarbon liquids for coal beneficiation are alsodiscussed in Foulke et al U.S. Pat. No. 2,150,917. Their halogenatedhydrocarbons include many with the disadvantages discussed above and, tosome extent, elaborated upon in O'Connell, Properties of Heavy Liquids,SME TRANSACTIONS, June 1963, pp. 126-132, which also lists still otherhalogenated hydrocarbons heretofore proposed as parting liquids.

The Foulke et al list also includes compounds such as trichloroethyleneand tetrachloroethane which chemically react with coal (carbontetrachloride is also in this category). Such parting liquids are notuseful because the parting liquid and the coal both become contaminated.

Contamination of the parting liquid makes the process economicallyimpractical because of the cost of purifying it and because of the lossof the parting liquid. A commercial scale operation cycles at leastseveral hundred tons per hour of the parting fluid, and loss of even asmall proportion of the liquid is accordingly economically significant.

Also, as discussed in the above-cited O'Connell paper, a relateddisadvantage of many of the heretofore proposed halogenated hydrocarbonsis that they adversely raact with common construction materials such asmild steel, rubber and other gasket materials, etc. as well aslubricants or decompose into compounds which will so react, especiallyif moisture is present. Both 1,2-difluoroethane and thefluorochlorocarbons we employ are much less inclined to react with suchmaterials, whether or not moisture is present, which is of self-evidentimportance.

Coals contaminated with halogen ions are also undesirable. In the caseof steaming coals this can cause boiler corrosion. Contaminated cokingcoals can undesirably alter the chemistry of the reactions in which theyare typically employed.

Another advantage of the present invention is that it can be employed incircumstances where the water content of the coal is high. For example,one application where our invention is particularly advantageous is inthe cleaning of slurry pond coals. Such coals, drip dried and suppliedto the beneficiation apparatus, may have a moisture content as high as15 percent.

In contrast coal beneficiation processes employing halogenatedhydrocarbon parting liquids such as those disclosed in Tveter cannot beemployed if the moisture content of the coal exceeds two percentaccording to the patentee. This makes such processes of littlecommercial value because only a few coals and anthracites have minedmoisture contents this low. Anthracites in toto account for less thanone percent of the annual coal production in this country.

Tveter does not stand alone in emphasizing that the presence of water ishighly deleterious in applications involving the use of halogenatedparting liquids. The same point is made in the above-cited Patchingarticle.

Still another advantage of our invention is that the specific gravity ofthe novel fluorochlorocarbons we employ and 1,2-difluoroethane can bereadily adjusted to make the specific gravity of the parting liquidoptimum for cleaning a particular coal.

For example, the nominal 1.5 specific gravity of trichlorofluoromethanecan be varied within a range of approximately 1.55-1.4 by modestvariations of the gravity separation bath temperature and pressure.

Lower specific gravities can be obtained by mixing a diluent such as alight petroleum fraction with the 1,2-difluoroethane orfluorochlorocarbon because of the inertness which such compounds displaytoward the organic materials in coal and toward the parting liquid andbecause the parting liquid is miscible in the light petroleum fraction.The same technique can also be employed to maintain the specific gravityof the parting liquid constant or to vary it in a controlled mannerunder changing ambient conditions.

Petroleum ether (a mixture of pentane and hexane) can be employed in anamount sufficiently small that the vapors from the parting liquid arenonexplosive and non-flammable to reduce the specific gravity of theparting liquid to as low as 1.3 at ambient temperature and pressure.Other liquids can be employed instead of petroleum fractions. Pentane,for example, has the properties which makes it useful for thispurpose--a low boiling point and a low heat of vaporization.

The use of hydrocarbon diluents to adjust the specific gravity of aparting liquid has heretofore been suggested in U.S. Pat. Nos. 2,165,607issued July 11, 1939, to Blow and 3,322,271 issued May 30, 1967, toEdwards. However, the diluents described in these patents--benzene(boiling point 80 plus °C.) and petroleum fractions with boiling pointsin the 70°-100° C. range--boil at too high a temperature for them to beusable in our coal cleaning processes which require that the diluentboil at a temperature as nearly as possible the same as that of thefluorochlorocarbon or 1,2-difluoroethane.

For this reason even the next higher homolog of pentane with its boilingpoint of 68° C. is undesirable. And if we employ a petroleum ether, wepreferably employ one having a boiling point toward the lower end of therange which such petroleum fractions have (40°-60° C.).

In general the lowest specific gravities that would be useful for ourpurposes are 1.40 to 1.30. Specific gravities in this range can beobtained by mixing with CCl₃ F, for example, from 7.7 to 16.4 weightpercent of a petroleum ether based on the total weight of the partingliquid.

Another advantage of the novel parting liquids we employ is that theyhave viscosities which are low even in comparison to other liquidsheretofore used as parting liquids in gravity separation processes asshown by the following table:

                  Table 1                                                         ______________________________________                                        Parting Liquid  Viscosity (Centipoises at 20° C.                       ______________________________________                                        Carbon tetrachloride                                                                           .969                                                         Tetrachloroethane                                                                             1.844                                                         Methylene bromide                                                                             1.09                                                          Water           1.00                                                          Tetrabromoethane                                                                              12.0                                                          Bromoform (CHBr.sub.3)                                                                        2.152                                                         -325 Mesh Magnetite                                                                           6-40 (average 12.0)                                            and water (1.6 specific                                                       gravity - production bath                                                     survey)                                                                      Trichlorofluoromethane                                                                        0.4                                                           ______________________________________                                    

Low viscosity is important because the velocity at which the particlesmove through the parting liquid and, therefore, the speed at whichbeneficiation proceeds is inversely proportional to the viscosity of theparting liquid--as the viscosity of the parting liquid is lowered, thespeed of the separation process increases.

In our process separation is completed in 1.0 to 5.0 minutes dependingupon the size consist of the coal and refuse even when the top size isless than 100 mesh. In contrast separation in the carbon tetrachloride,bromoform, and ethylene dibromide typically used in standard washabilitystudies may require 2 to 24 hours.

Other advantages of low viscosity parting liquids are discussed in U.S.Pat. No. 3,098,035 issued July 16, 1963, to Aplan.

Our novel parting liquids are also superior to others heretoforeproposed and employed because they have lower surface tensions. For theliquids listed above, the surface tensions are:

                  Table 2                                                         ______________________________________                                        Parting Liquid   Surface Tension (dyne/cm)                                    ______________________________________                                        Carbon Tetrachloride                                                                           27                                                           Tetrachloroethane                                                                              36                                                           Methylene Bromide                                                                              40                                                           Water            75                                                           Bromoform        41.5                                                         -325 Mesh magnetite                                                                            75                                                            and water                                                                    Trichlorofluoromethane                                                                         18                                                           ______________________________________                                    

Surface tension is important because wetting ability is a function oflow surface tension. If the coal is not completely wetted by the partingliquid, air will be trapped on both the coal and gangue particles,making them tend toward a common density. As a consequence, separationbecomes more difficult and less efficient.

The problem is particularly acute for particle sizes of one millimeteror less. Yet the presence of such particles may not be avoidable as inthe recovery of coal from slurry ponds, for example.

The novel parting liquids we employ have surface tensions so low thatthe free surfaces of even very small particles, including micro cracks,are essentially instantaneously wetted. This is one reason that we areable to attain separation efficiencies which often exceed thosepredicted by theoretical washability curves.

Another advantage of our invention is that there is no need to separatethe raw coal into large and small particle consists as is necessary inpresently employed coal cleaning processes. Lumps of 5-6 inches andlarger in diameter can easily be handled as can those 325 mesh andsmaller although separation times are longer (up to several minutes) forthese smaller particles.

In general, therefore, the only restrictions on particle size are thoseimposed by the material handling equipment available and by the size towhich the raw coal must be reduced to liberate the impurities necessaryto meet product specifications.

Also, essentially all of the parting liquid can be recovered. This notonly makes the process viable from the economics viewpoint but has adecidedly favorable environmental impact. No contaminated water or otherecologically detrimental chemicals are discharged from the process.

Other advantages of the novel parting liquids we employ are that theyare non-flammable, odor free, and non-toxic.

Yet another advantage of our process is that, as far as we can observe,there is no tendency for slimes to form even in circumstances wheresignificant amounts of clays are present. This is important because thecontrol of slimes in other gravity separation processes is a pressingproblem as evidenced by the discussions of the problem in theabove-identified Aplan patent and in U.S. Pat. No. 2,136,074 issued Nov.8, 1938, to Crawford et al.

Nor have we seen any evidence of flocculation and/or rafting. Thatflocculation can be a problem in other gravity separation processes isapparent from Tveter and U.S. Pat. No. 3,308,946 issued Mar. 14, 1967,to Mitzmager et al.

The only reference known to us which suggests that a fluorochlorocarbonbe used as a parting liquid is U.S. Pat. No. 3,322,271 issued May 30,1967, to Edwards. This patent avers that1,1,2-trichloro-1,2,2-trifluoroethane can be used as a parting liquid toseparate tea stalks from tea leaves although there is nothing in thepatent such as a working example which shows that this can actually bedone.

Even more important the teachings of Edwards would lead one to believethat this compound would not be useful for gravity separation of coal.The patentee suggests that 1,1,2-trichloro-1,2,2-trifluoroethane and theother liquids listed in the patent (trichloroethylene,perchloroethylene, and carbon tetrachloride) are all equivalents asparting liquids. However, all of these other liquids are known todissolve and chemically react with coal which is highly undesirable forthe reasons discussed above. As it is associated in the Edwards patentonly with liquids which are not suitable for coal beneficiation, onewould not expect 1,1,2-trichloro-1,2,2-trifluoroethane to be useful forthat purpose.

A fortiori, there is nothing in Edwards which would even remotelysuggest that 1,1,2-trichloro-1,2,2-trifluoroethane would have theunexpected advantages in cleaning coal which we have found it does.There is nothing in the patent to indicate that this compound wouldeffect the removal of organic sulfur from coal, that it would causewater associated with coals of high water contents to report to thesinks or rejects, or that the liquid could be recovered from the coal inalmost quantitative proportions with only very modest expenditures ofenergy.

There is also an allegation that "fluorine substituted . . . alkylcompounds" can be used as parting liquids in U.S. Pat. Nos. 3,802,632issued Apr. 9, 1974, and 3,746,265 issued July 17, 1973, both to Dancy.However, no specific compounds are named; and, as discussed above, onlya handful of the many compounds meeting this description are suitablefor our purposes.

Although not essential, we prefer to prewet or condition the coal to becleaned with a mixture of a fluorochlorocarbon or 1,2-difluoroethane anda ionic surface active agent prior to introducing it into the gravityseparation bath. This conditioning with the combination of ionic surfaceactive agent and fluorinated hydrocarbon has unexpectedly been found tocause significant proportions of the surface water which would beexpected to remain with the coal to instead report to the sinks.

The removal of water to the sinks is particularly important in theprocessing of coals of higher water content as the redistribution of thewater in the system can simplify, and even eliminate, subsequentdewatering of the coal.

More specifically, coarse product coal typically has a moisture contentof 4-7 percent while that of fine product coal can range from 10-30 pluspercent. Moisture contents in the latter range and the upper end of thefirst-mentioned range both reduce the efficiency with which the coal canbe burned and generate handling problems. For example, entire carloadsof coal of such moisture content can freeze into a single lump infreezing temperatures, making it tremendously difficult to unload andhandle the coal.

Larger sizes of coal are conventionally dewatered on shaker screens orconical screens. Smaller size consists are customarily dewatered in abasket type centrifuge and still smaller particles in solid bowlcentrifuges. Alternatively, coal can be thermally dewatered; that is,heated to a temperature high enough to evaporate part or all of themoisture. Fluidized bed dryers are customarily employed for thispurpose.

By reducing the need for dewatering by the techniques just described ournovel coal cleaning process generates corresponding savings in capitalinvestment for equipment, in operating costs, and in expenditures ofenergy.

Another advantage of conditioning the coal to be cleaned with our novelcombination of 1,2-difluoroethane or a fluorochlorocarbon and a surfaceactive agent is that this results in a greater reduction in the sulfurcontent of coal than can be obtained by other processes for which dataon reductions in sulfur content have been reported. Maximum removal ofsulfur is important because the sulfur contents of coals found in theUnited States range as high as seven to ten percent while, preferably,coking coals contain no more than 1.3 percent sulfur, and governmentstandards proposed for the late 1970's would limit many steaming coalsto a sulfur content in the range of 0.5 percent.

Three types of sulfur can be present in coal. These are:

(a) Pyritic sulfur--FeS₂, density 4.9 g/cm³ ;

(b) Sulfate sulfur--usually calcium sulfate resulting from the reactionof water and pyrites to form sulfuric acid and the subsequent reactionof the acid with calcium carbonate associated with the coal; and

(c) Organic sulfur--sulfur bound with carbon atoms in the coal matrixinto molecules of organic character. Discrete compounds have not as yetbeen positively identified, but organic sulfide and sulfone linkagesappear to be present. In chemical analyses of coal, total, pyritic, andsulfate sulfur are measured; and the difference between the latter twoand total sulfur is reported as organic sulfur.

Pyritic sulfur particles as small as 0.01 inch in diameter are common.As discussed above, even particles of this minute size can beefficiently removed by our novel process when they are released from thecoal because the excellent wetting properties of the parting liquids weemploy make it feasible to use a size consist of this magnitude in thebeneficiation process. In contrast, conventional hydrobeneficiationbecomes inefficient to an increasing and dramatic degree as particlesizes decrease below 0.2 inch in diameter and becomes totally inoperableat particle sizes lower than 0.02 inch in diameter. Therefore,hydrobenefication techniques are inherently incapable of removing asmuch of the pyritic sulfur which may be present in a particlar raw coalas our process.

We have also found that, surprisingly, a reduction in organic sulfur canbe obtained by our novel process. This has been ascertained byevaporating used parting liquid to dryness and making an infraredanalysis of the residue. There is evidence that some organic sulfur alsoreports to the sinks (gangue) in our process.

Hydrobeneficiation, in contrast, does not alter the organic sulfurconcentration of the raw coal under any conditions.

In fact, to our knowledge, the only heretofore available techniques forremoving organic sulfur from coal are pyrolytic. Such techniques are notusable in cleaning coal generally because of the energy expended inheating large tonnages of coal to the requisite temperature and becauseof the alteration in the chemical composition and the structure of thecoal which results.

We have also found that the use of surface active agents in our novelprocess increases the quality of the separation when wet coal--that is,coal with a moisture content as high as 25 percent--is being cleaned.This is entirely unexpected because of the insistence by Tveter thathalogenated hydrocarbon/surfactant mixtures cannot be used to clean coalwith a moisture content of more than two percent; that is, that they areonly useful in cleaning dry coal.

Water effects other gravity separation type coal cleaning processesbecause it forms on the coal particles a thin film to which smallparticles of more dense foreign material can adhere. This creates"agglomerates" which may have a specific gravity greater than theparting liquid, causing them to report to the sinks (gangue) rather thanthe floats (product coal) if the coal particles are small. Conditioningthe coal as described above apparently makes our novel parting liquidscapable of rupturing these thin films, thus preventing the formation ofagglomerates.

This phenomenom is particularly apparent in the reclaiming of coal fromslurry ponds. When cleaned in accord with the technique just described,even ultra-fine clay particles are separated from the coal.

Also, there is evidence that part of the pyritic sulfur present in somecoals is bonded to the coal particles by forces (probably electrostaticand less likely thin film) which can be neutralized by thosecombinations of parting fluids and additive described above. We are inany event able to obtain reductions in pyritic sulfur content whichindicate that pyrite particles smaller than those liberated by finegrinding are being separated from the raw coal.

Among the surface active agents we have successfully employed are thefollowing:

                                      Table 3                                     __________________________________________________________________________    Surface Active Agent                                                                     Type Composition      Manufacturer                                 __________________________________________________________________________    Aerosol    Anionic                                                                            Dioctyl ester of sulfosuccinic acid                                                            American Cyanamid                            OT-100                                                                        Aerosol    Anionic                                                                            Dioctyl ester of sulfosuccinic acid                                                            American Cyanamid                            OT-75                                                                         Cal Supreme                                                                              Cationic                                                                           Dioctyl ester of sulfosuccinic acid                                                            Penwalt-Caled Company                        Perk-Sheen                       Adco, Inc.                                   Super-Cal  Anionic                                                                            Dodecyl benzene sulfonic acid salt                                                             Penwalt-Caled Company                        Pace-Perk  Anionic                                                                            Dodecyl benzene sulfonic acid salt                                                             Penwalt-Caled Company                        Strodex Super V-8                                                                        Anionic                                                                            Complex organic phosphate esters                                                               Dexter Corporation                           Strodex P-100                                                                            Anionic                                                                            Complex polyphosphate ester acid                                                               Dexter Corporation                                           anhydride                                                     Witconate P10-59                                                                         Anionic                                                                            Amine Salt of dodecylbenzene                                                                   Witco Chemical Corporation                                   sulfonic acid                                                 Witcomine  Cationic                                                                           1-Polyaminoethyl-2n-alkyl-2-                                                                   Witco Chemical Corporation                                   imidazoline                                                   Triton Gr-7M                                                                             Anionic                                                                            Dioctyl sodium sulfonate plus                                                                  Rohm and Haas                                                solvent                                                       __________________________________________________________________________

Anionic surface active agents are preferred as are those which are asingle compound rather than a blend. Blends tend to be less effective ona unit weight basis, apparently because they tend to emulsify the wateron the coal rather than removing it to the sinks.

Small amounts of the surface active agent are lost, probably with thewater removed to the rejects. However, the cost of lost material is notexpected to exceed $.30 per ton of coal; it will in general besubstantially less.

The amount of surface active agent used will depend upon the particularadditive which is selected and the size consist and moisture content ofthe coal, but will typically range from six pounds per ton for ultrafinecoals with high moisture contents down to 0.03-0.05 pounds per ton forcoarser coals of lower moisture content.

Agitation of the coal in the conditioning step has also been found to beadvantageous. This can be accomplished by mechanical folding of theliquid, coal mixture.

We can also employ No. 4 or No. 6 fuel oil or certain alkyl amines assurface active agents instead of the compositions just described.Mixtures employing these compositions produce essentially the sameresults as those using compositions more conventionally thought of assurface active agents though less effectively.

No. 4 and No. 6 fuel oils are both employed in an amount ranging from0.5 to 6 pounds per ton of coal.

Alkyl amines can be employed in amounts ranging from 0.05 to 0.5 poundsper ton of coal. Examples of satisfactory amines are: diethylamine,ethylene diamine, and monoethyl amine.

The use of surfactants in gravity separation processes has heretoforebeen discussed in Blow, Tveter, Aplan, and Foulke et al 2,208,758, andin U.S. Pat. No. 2,899,392 issued Aug. 11, 1959, to Schranz. The Blowand Schranz patents, however, are not concerned with the cleaning ofcoal; and there is nothing in either patent which would leave one tobelieve that surfactants could be used to advantage in coal cleaningprocesses. Foulke et al chose surfactants which would fix the water filmon the material being recovered rather than freeing it from thatmaterial for removal to the sinks. This class of surfactants hascompletely different properties than those we employ and, moreover,properties we consider undesirable.

The parting liquids with which Aplan is concerned are aqueoussuspensions of solid particles. The patent discloses nothing regardingparting liquids which are combinations of 1,2-difluoroethane or liquidfluorochlorocarbons and surface active agents and their advantages.

Much the same is true of Tveter. The parting liquids disclosed in thatpatent are not fluorochlorocarbons. The latter have a number ofadvantages over the Tveter parting liquids as discussed above; andmoreover, there is nothing in the patent which would lead anyone tobelieve that any advantage would accrue from combining surface activeagents with such parting liquids, let alone that this would increase thesulfur or fine particle removing capabilities of such compounds.

Furthermore, Tveter is concerned in his use of surfactants only withinhibiting floc formation. This would not lead one to use a surfaceactive agent in the manner and for the purposes we do.

Furthermore, the foregoing patents are for the most part concerned withthe use of surface active agents for slime control and to stabilizeheavy medium suspensions of solids and not with the removal of waterfrom the product to the rejects in a gravity separation process.

Nor is the surface active agent employed in a conditioning step as it isin our process. It is instead added to the parting liquid in the gravityseparation bath. Our technique has the advantage that amount, exposure,and time factors can be optimized independent of the separation stage.

In another aspect out invention resides in the provision of novelimproved techniques for moving coal and other solids from place-to-placeand, more particularly, to the use of 1,2-difluoroethane andfluorochlorocarbons as described above for this purpose.

Coal is commonly transported in the form of an aqueous slurry becausethis is the product of the coal beneficiation process.

We have now discovered that these advantages can be retained andadditional advantages obtained by employing a 1,2-difluoroethane orfluorochlorocarbon carrier.

Specifically, because these compounds have lower viscosities than water,slurries in which they are used as the carrier liquid can be pumped withless power than water-based slurries with the same solids content. Or,viewed otherwise, the solids content of the slurry can be increased fora given power output. From both points-of-view the significant factor isthat the cost per unit weight of moving the coal or other solids islower.

In addition, because the liquids we employ are chemically inert in mostcircumstances, the corrosion problems attendant upon the use of water incircumstances where soluble minerals are present are avoided.Furthermore, our carrier liquids do not cause the flocculation problemswhich water may.

Also, as when they are used in our novel beneficiation process, theirlower latent heat of vaporization and lower boiling points permit theliquids we employ to be removed at the terminal point with less energyand therefore at a lower cost than water.

Even at that, however, we find it necessary to add heat to the slurry torecover the carrier liquid. Also, a vacuum or gas purge is required as,otherwise, so much carrier liquid will remain in the pores of the coalparticles as to make the process impractical.

The precise temperature to which materials are heated to remove acarrier liquid associated therewith in our novel process fortransporting coal and in the other novel processes described hereinwhich employ a carrier liquid removal step will vary fromapplication-to-application and will depend upon a number of factors.Among these are the boing point of the fluorochlorocarbon, the removalrate required to maintain equilibrium in the system, etc. In a typicalapplication using trichlorofluoromethane, however, a drying or liquidremoval temperature of 100° F. (25° F. above the boiling point of theliquid) will be employed.

In addition, because of the physical characteristics of the carrierliquids we employ, coal particles do not tend to pack in the carrierliquid in the extent they do in water. Accordingly, even after it hasremained static for an extended period, flow can be initiated almostinstantaneously in a slurry formed according to the present invention.

Numerous patents disclose techniques for transporting aqueous slurriesof coal. Among these are U.S. Pat. Nos. 449,102 issued Mar. 31, 1891, toAndrews; 2,128,913 issued Sept. 6, 1938, to Burk; 2,346,151 issued Apr.11, 1944, to Burk et al; 2,686,085 issued Aug. 10, 1954, to Odell;2,791,471 issued May 7, 1957, to Clancey et al; 2,791,472 issued May 7,1957, to Barthauer et al; 2,920,923 issued Jan. 12, 1960, to Wasp et al;3,012,826 issued Dec. 12, 1961, to Puff et al; 3,019,059 issued Jan. 30,1962, to McMurtie; 3,073,652 issued Jan. 15, 1963, to Reichl; and3,524,682 issued Aug. 18, 1970, to Booth.

Other carrier liquids have been proposed. These, typically, are liquidpetroleum fractions used alone or with water, etc. Exemplary ofprocesses employing such carrier liquids are those disclosed in U.S.Pat. Nos. 1,390,230 issued Sept. 6, 1921, to Bates; 2,610,900 issuedSept. 6, 1952, to Cross; 3,129,164 issued Apr. 14, 1964, to Cameron;3,190,701 issued June 22, 1965, to Berkowitz et al; 3,206,256 issuedSept. 14, 1965, to Scott; 3,377,107 issued Apr. 9, 1968, to Hodgson etal; and 3,359,040 issued Dec. 19, 1967, to Every et al.

The use of a heavy liquid as a carrier for coal is suggested in U.S.Pat. 2,937,049 issued May 17, 1960, to Osawa. However, in the Osawatechnique the carrier liquid is employed to float the coal to the top ofa vertical shaft and is therefore of limited applicability. Furthermore,the heavy liquids proposed by this patentee (aqueous dispersions of siltplus pulverized pyrite, hematite, limonite, magnetite, ferrosilicon, orgalena) would be unsuitable for pipeline transport because they arehighly abrasive if for no other reason.

Wasp (U.S. Pat. Nos. 3,637,263 issued Jan. 25, 1972, and 3,719,397issued Mar. 6, 1973) does suggest that aqueous coal slurries containingmagnetite, magnesite, barites, hematite, etc. can be used for thepipeline transportation of coal. However, we consider this techniqueinferior because of the abrasion problem discussed above. Also, therecovery of the carrier at the terminus, the drying of the coal, and thereturn of the carrier liquid is a much more complex and expensiveprocedure than we find necessary.

There is one patent of which we are aware that suggests using afluorochlorocarbon as the carrier for a coal slurry. This patent is U.S.Pat. No. 3,180,691 issued Apr. 27, 1965, Wunsch et al.

However, one of the fluorochlorocarbons which Wunsch et al propose touse (dichlorodifluoromethane) boils at -30° C. Accordingly, the pressurein the pipeline must be kept at 77 psig simply to keep thefluorochlorocarbon liquid at room temperature (72° F.) and at 106 pluspsig to keep the carrier liquid at the easily reached summertimetemperature of 95° F. We consider this undesirable because of the energyrequired, the problem of sealing the line against leakage engendered bythe large pressure differential, and the difficulty there would be ineffecting movement of the solids if any significant amount of thecarrier were lost.

Wunsch et al also suggest that trichlorofluoromethane can be used as thecarrier liquid in their coal transport process. We disagree because, intheir process, the carrier liquid is removed from the solids byevaporation at ambient temperature and pressure which means that thelatent heat of vaporization must be supplied by the solids and from theambient surroundings.

As a practical matter, the bulk of the heat must come from the lattersource. For example, if the solids were to supply all of the sensibleheat required to evaporate trichlorofluoromethane from a slurry composedof equal parts by weight of carrier and solids, the solids would have todecrease 283° F. in temperature, an obvious impossibility as thetemperature of the solids may not be much above ambient temperature whenthe slurry reaches the terminus.

Trichlorofluoromethane vaporizes at ca. 75° F. at atmospheric pressure.As a coal transport process has to be capable of operating on atwenty-four hour basis to be of any practical value and as thetemperature differential between the ambient surroundings and theboiling point of the carrier liquid must be significant for evaporationof the liquid to proceed at an appreciable rate, the Wunsch et alprocess using trichlorofluoromethane as the carrier liquid would beoperable only where the round-the-clock ambient temperature at theterminus exceeds 75° F. by a significant margin. As such conditionsexist only in controlled environments and in a few tropical locations(see, for example, Handbook of Fundamentals, American Society ofHeating, Refrigerating, and Air Conditioning Engineers, 345 East 47thStreet, New York, N.Y., 1972, pp. 667-688), the process in question haslittle if any practical value.

In contrast, our novel process for transporting coal is essentiallyindependent of the ambient temperature at the terminus. It can be usedin Arctic and tropical conditions and in any conditions rangingtherebetween.

Another disadvantage of the Wunsch et al process iftrichlorofluoromethane or a comparable carrier liquid is employed isthat recovery of the carrier by evaporation under ambient conditions,alone, will leave a large proportion of the carrier liquid in the poresof the solids. In the case of a typical coal this would be on the orderof six pounds of carrier per ton of coal. As trichlorofluoromethanecurrently sells for $0.30 per pound, the cost of unrecovered carrierliquid would be $1.80 per ton of coal transported. This would make theprocess economically impractical.

In contrast, our novel use of a purge at the terminus results in therecovery of essentially all the carrier liquid from the slurry. Becauseof this and other factors, our novel process is highly viable from theeconomic viewpoint. For example, we can typically reduce the carriercontent of the coal to on the order of 20 percent by drip drying, atechnique not disclosed in Wunsch et al. Drip drying can reduce theenergy required to remove the carrier liquid by as much as 60 percent ormore depending upon the particular application of our invention.

It is sometimes advantageous to incorporate additives into coal tomodify its properties. For example, recent studies have shown that theaddition of quicklime (chiefly calcium oxide) or calcined dolomite(chiefly calcium-magnesium oxide) to coal brings about a significantreduction in the sulfur content of the combustion products generatedwhen the coal is burned.

In still another aspect our invention involves a novel technique bywhich a virtually unlimited variety of additives can be easily,economically, and uniformly dispersed in coal.

Briefly, we dissolve or disperse the additive or additives in afluorochlorocarbon as described above or 1,2-difluoroethane; immerse thecoal in or spray or drench it with the carrier, additive composition, orotherwise effect contact between the coal and the composition; and themremove the carrier, leaving the additive absorbed in and/or adsorbed onthe free surfaces of the coal particles.

In processes also involving a coal cleaning step the additive can insome cases be dispersed in the parting liquid bath in the gravityseparator or in the parting liquid mixed with uncleaned coal in aconditioning step. Alternatively, the additive can be distributed in aunit downstream from the gravity separator.

Our novel technique for incorporating additives is highly effectivebecause the low viscosity and surface tension of the fluorochlorocarbonor 1,2-difluoroethane carriers permit them to penetrate and transportthe additives into even the smallest pores and micro cracks in the coalparticles.

Another advantage of our novel dispersing process, attributable to thephysical properties of the carrier liquid, is that the carrier can beeasily, inexpensively, and essentially completely recovered after thedispersion of the additive has been completed.

Also, the process can be carried out at ambient temperature and atatmospheric pressure. Because of this and the lack of toxicity andcorrosiveness possessed by our carrier liquids, exotic and expensiveequipment is not required.

Yet another advantage of our novel technique, in a multi-step operation,is that the coal need not be freed of the parting liquid employed in thecleaning step before the additive is dispersed. This is because both thecarrier and parting liquids may be 1,2-difluoroethane or the same, orcompatible, fluorochlorocarbons, making removal of the parting liquidunnecessary.

Yet another advantage of our novel method of dispersing additives isthat no water is introduced into the system. This is important, as anexample, in the addition of quicklime to coal to reduce sulfuremissions. The reaction

    CaO+H.sub.2 O→Ca(OH).sub.2

is highly exothermic and, also, reduces the availability of one of thereactants needed for the subsequent sulfur removal reaction. By avoidingthe introduction of water into the product our novel process insuresthat the reactant is available in its more reactive form to the maximumextent.

Other exemplary applications where our novel technique for dispersingadditives can be employed to advantage are the dustproofing andwaterproofing of coal and the addition of a binder as a preliminary oflow-temperature briquetting.

The addition of a dustproofing agent is particularly important. Intransporting coal of smaller size consists by rail 1-10 percent of thecoal is not uncommonly lost between the preparation plant and thepoint-of-use. By dustproofing coal in accord with our invention, thisloss can be substantially reduced.

One exemplary technique for dustproofing coal in accord with the presentinvention involves the distribution of fuel or residual oil on the coalto coalesce the finer particles into agglomerates. Amounts in the rangeof 0.05 to 0.5 percent based on the weight of the coal will typically beemployed, depending upon the size consist of the coal.

The dustproofing agent is first dispersed in the fluorochlorocarbon or1,2-difluoroethane carrier in an amount ranging from 0.1 to 5 weightpercent based on the weight of the carrier. The coal is immersed in thecomposition and the carrier removed by evaporating it.

The removal of the carrier leaves the oil residue on the coal surface.This causes agglomeration, substantially reducing the proportion ofdust-size particles present.

The application of our novel process for dispersing additives to thewaterproofing of coal is also important.

As indicated above, as mined coals may have moisture contents as high as29-33 percent. If these coals are shipped with a moisture content ofthis magnitude, almost one-third of the freight charges paid by theshipper are for transporting water. To compound the problem, coals withwater contents of the high magnitudes in question are typically youngWestern coals and must be shipped relatively long distances to thepoint-of-consumption.

However, it has not heretofore been practical to remove the water fromthe coal before shipping it. Readsorption of water often occurs sorapidly, especially if the coal is exposed to precipitation, thatspontaneous combustion occurs because of the build-up in temperature dueto the heat of adsorption. Entire carloads of coal have been destroyedin this manner.

In accord with our invention the coal is dried and the free interior andexterior surfaces coated with a waterproofing agent such as a crude oilor other heavy bitumen by immersing the dried coal in or otherwiseintimately contacting it with a dispersion of the waterproofing agent in1,2-difluoroethane or one of the fluorochlorocarbons listed above. Thecarrier liquid is then removed, leaving a thin film of the waterproofingagent on the exterior surfaces of the coal and on those inner surfaceswhich are accessible to liquids. This keeps water from readsorbing ontothe surfaces accessible to it, and spontaneous combustion cannot occur.

Further benefits are that oxidation and slaking of the coal areeffectively inhibited by the coating of waterproofing agent as is thefreezing together of the coal under low ambient temperature conditions.All of the foregoing benefits are of course realized in the storing ofcoal as well as in transporting it.

Processes for treating coal to keep the particles from freezing togetherare known. One such process is described in U.S. Pat. No. 3,794,472issued Feb. 26, 1974, to Macaluso et al. However, in the Macalusoprocess, the coal is sprayed with substantial quantities of water (up to68 percent of the coating composition). This water would be absorbed bythe coal to a large extent. Therefore, even if the coal particles werethereafter surrounded with films which would entrap surface water andkeep it from freezing the particles together, the other problemsappurtenant to the presence of absorbed water, such as spontaneouscombustion, would not be solved as they are by our novel waterproofingtechnique which not only does not add water to the coal but prevents thecoal from reabsorbing water.

The making of briquettes, mentioned above, is another importantapplication of our additive dispersing process.

In briquetting coal, small particles treated with a binder such as No. 6fuel oil by use of the technique just described are compacted in a moldat room temperature and under moderate pressure (2000 to 5000 psidepending upon the binder, size consist, and moisture content). Theresulting briquettes are stable, even under relatively high impacts, andthe process is economical.

U.S. Pat. No. 3,027,306 issued Mar. 27, 1962, to Muschenborn et aldiscloses a process for making briquettes which, like ours, involves agravity separation step and the use of a binder. However, Munschenbornet al use carbon tetrachloride or a magnetite suspension as the partingliquid. These have major disadvantages, discussed above, andfurthermore, would not be useful as a carrier for the binder as ournovel parting liquids are. In addition, Munschenborn et al find itnecessary to coke the coal before cleaning it, a step we need notemploy.

Additives can be dispersed on solids other than coal by the process justdescribed. For example, this process can be used to dedust sinksgenerated in a coal cleaning operation, ash generated in burningsteaming coal, etc. Still other solids can be treated by our process aswill be readily apparent to those skilled in the relevant arts.

Rejects can be treated in the gravity separator, in a conditioning step,or in a separate unit after they are removed from the gravity separator.In applications which do not involve a cleaning operation the solids arenecessarily treated in a unit provided especially for this purpose.

As indicated above, a virtually unlimited range of materials can bedispersed by our process. One restriction on the additive is that it besoluble or otherwise uniformly dispersable in the carrier liquid. Asecond limitation in some cases is that the additive not reactchemically with the carrier liquid.

In yet another aspect our invention resides in the provision of a novel,integrated process for handling coal from the mine face to a consumptionpoint or other terminus in which the beneficiation and slurry transporttechniques described above are employed.

Mining machines of the hydraulic or continuous type may be employed inour novel system. The mined coal is crushed and transported away fromthe mine face in a slurry with 1,2-difluoroethane or one of the liquidfluorochlorocarbons identified above rather than by the conventionalbelt, shuttle car, or other mechanical arrangement. Thefluorochlorocarbon or 1,2-difluoroethane and additive system is alsoemployed for dust supression at the mine face as such compounds are moreeffective than water for this purpose. In addition, thefluorochlorocarbon or 1,2-difluoroethane, perhaps with an appropriateadditive such No. 6 fuel oil and/or one or more alkyl amines, can reducecutter wear and energy requirements.

The coal slurry can be pumped to a primary cleaning plant, typicallylocated in the mine itself. Here, an initial gravity separation of theforeign matter and raw coal is made as described above.

The gangue separated from the coal is stripped of parting liquid,optionally treated with a dust suppressant, and conveyed to a mined-outarea of the mine.

The floats from the initial separation step, slurried in the partingliquid, are pumped to a final treating plant, typically locatedaboveground at the mine mouth. There the coal is ground to a size whichwill release the maximum amount of foreign material and subjected to asecond gravity separation, again using a fluorochlorocarbon or1,2-difluoroethane parting liquid in accord with the principles of thepresent invention.

Sinks from this step are stripped of parting liquid and conveyed to adisposal area. They may first be treated to inhibit the generation ofacidic ground water and/or other ecologically undesirable phenomena.

Floats (or, product coal) from the final cleaning step, again slurriedwith the parting liquid, may be pumped to the point of consumption,typically a power generating plant, and stored. Prior to use they arestripped of the parting/carrier liquid and, if necessary, ground to asmaller size consist.

Liquid stripped from the coal in the final preparation step can beemployed to slurry ash from the power plant furnace bottoms and fly ashprecipitators and convey it back to the final cleaning point. Here, theash is stripped of the carrier, treated as required, and conveyed to therefuse area with the gangue separated in the final cleaning step. Theliquid is recycled, typically to the raw coal slurry pump and to themine face.

The advantages of using 1,2-difluoroethane or a fluorochlorocarbon as adust suppressant at the mine face were discussed above. Because of theseand the other advantages of our novel materials such as lack ofcorrosiveness, toxicity, and flammability, explosion hazards are reducedand safety otherwise promoted by our novel system.

Explosion hazards are also reduced because the system is essentiallyclosed beginning at the mine face. Accordingly, methane and othercombustible gases (i.e., firedamp) can be captured and removed from themine face as well as from the coal during beneficiation, transportation,and storage to a point where they can be safely disposed of or recoveredif the concentration warrants.

Another potential advantage of the novel coal mining and handling systemjust described is that only a small fraction of the gangue is removedfrom the mine. This materially reduces the material handling capacityand energy required and, also, the aboveground disposal problems.

A related advantage is that the disposal of refuse from the powergenerating plant or other consumer of the product coal is simplified.

Also, if quicklime is mixed with the coal to suppress sulfur emissionsas described above, the refuse from the generating plant will tendtoward a basic pH. The presence of this refuse in the refuse pile withpyrites and other acid forming rejects from the cleaning operations willtend to neutralize any acids formed by water contacting the refuse pile,thus reducing the ecological hazards which such refuse piles commonlypresent.

Other related advantages of our invention are that the conveyor systemin the mine occupies less room and can more conveniently be relocatedand extended than conventional conveyor systems.

A further significant advantage is that the coal is protected againstoxidation from the time it is mined until it is consumed. This gives itpotentially better combustion characteristics than conventionallyhandled coal and, also, minimizes the losses in heating value which canoccur through oxidation.

Furthermore, the area required for coal storage at the point ofconsumption is considerably reduced as is the fire hazard; and there isno need for compaction or dust suppression.

In addition all the underground and surface activities, includingmaterial handling and transportation, are independent of weather andclimate.

Other advantages of our novel, integrated, coal handling and processingtechnique, attributable to the nature of the parting, carrier liquids weemploy, were described above in conjunction with the coal cleaning andtransporting aspects of the invention.

Another important advantage of our novel system is that the advantagesat one stage carry over to other stages. For example, because the use ofa fluorochlorocarbon or 1,2-difluoroethane in conveying the product coalfrom the final cleaning station to the point of consumption inhibitsoxidation, the coal may be ground for the cleaning step to a sizeconsist which will optimize the separation of pyrites and other foreignmaterial from the coal without regard to the increase in surface areaand the accompanying potential for chemical reaction which results.

It will be appreciated by those conversant in the relevant arts that ournovel coal handling and processing system is not limited in applicationto operations where the coal is to be burned at the mouth of the mine.The coal recovered from the final cleaning plant can instead bytransported elsewhere in slurry with the parting liquid or, after thelatter is stripped from the coal, by conventional modes of transport.

Also, it will be readily apparent to those to whom this is addressedthat, with easily visualized modifications, the novel integrated systemjust described can be used in association with open pit as well as deepmines.

Yet another important advantage is that the system can, to a largeextent, operate automatically and unattended.

In yet another aspect our invention resides in certain novel techniquesfor recovering from coal and refuse the fluorochlorocarbons or1,2-difluoroethane employed as carriers and as parting liquids. Thefluorochlorocarbon or 1,2-difluoroethane may be stripped from the coalor refuse by a vacuum purge or simple evaporation. It is thencompressed, condensed, purged of noncondensible gases, and recycled.

Alternatively, the hydrocarbon is stripped from the coal or refuse byevaporation and an air purge. The gas, vapor mixture is compressed andcondensed, converting the fluorochlorocarbon or 1,2-difluoroethane to aliquid and leaving the air as a gas. Additional fluorochlorocarbon or1,2-difluoroethane can be recovered by compressing and refrigerating thenoncondensibles, and the purge air can by recycled.

An air purge is also employed in a third recovery technique. The air andfluorochlorocarbon or 1,2-difluoroethane mixture is compressed and/orcondensed and the noncondensible vapor stream contacted with a fuel oilor any other liquid capable of selectively absorbing the hydrocarbon.The noncondensible gases are recycled or rejected, and the fluid isheated to vaporize and release the fluorochlorocarbon or1,2-difluoroethane. The latter is compressed and condensed, theabsorption fluid is cooled to restore its absorption capabilities, andthe sensible heat is recovered.

Advantages of these novel techniques for recovering the parting, carrierliquids are that they are economical and efficient. Also, the equipmentin which the recovery is effected can be readily integrated with theapparatus in which the other of the process steps described herein arecarried out.

Vacuum and air purges are, as such, known as is the use of an "oil" toseparate one gas from another by selective absorption as shown by thefollowing U.S. Pat. Nos. 2,429,751 issued Oct. 28, 1947, to Gohr et al;3,392,455 issued July 16, 1968, to Kingsbaker et al; 3,439,432 issuedApr. 22, 1969, to Bellinger et al; 2,497,421 issued Feb. 14, 1950, toShiras; 2,614,658 issued Oct. 21, 1952, to Maher et al; 2,652,129 issuedSept. 15, 1953, to Benedict; 2,710,663 issued June 14, 1955, to Wilson;2,870,868 issued Jan. 27, 1959, to Eastman et al; 2,961,065 issued Nov.22, 1960, to Helm et al; and 3,208,199 issued Sept. 28, 1965, to Pruiss.

However, none of these patents disclose a method for recoveringfluorochlorocarbons or 1,2-difluoroethane or techniques which, even ifthey could somehow be adapted to this use, would have the advantagesours give. The same is true of the heretofore proposed techniques forrecovering organic fluorine compounds described in the following U.S.Pat. Nos. 2,508,221 issued May 16, 1950, to Calfee et al; 3,013,631issued Dec. 19, 1961, to Johnson; 3,197,941 issued Aug. 3, 1965, toColton et al; 3,236,030 issued Feb. 22, 1966, to Von Tress; 3,581,466issued June 1, 1971, to Rudolph et al; 3,617,209 issued Nov. 2, 1971, toMassonne et al; and 3,680,289 issued Aug. 1, 1972, to Rudolph et al.

Yet another suggestion that halogenated hydrocarbons such as acetylenebromide can be recovered by selective absorption is found in anunpublished article by Tveter and O'Connell entitled Heavy Liquids forMineral Beneficiation. However, our technique for recoveringfluorochlorocarbon and 1,2-difluoroethane parting liquids differs in anadvantageous manner in that we are able to recover from the absorbingmedium significant amounts of the sensible heat added to the medium torelease the parting liquid from it.

The novel recovery techniques described above are of course of generalapplicability. That is, they can be used to recover fluorochlorocarbonsand 1,2-difluoroethane from other solids besides coal, rejects from acoal cleaning operation, and ash generated by burning coal.

From the foregoing it will be apparent to the reader that one importantand primary object of our invention resides in the provision of novelimproved methods for beneficiating coal to separate the coal fromforeign material associated therewith.

Related and also important but more specific objects of the inventionreside in the provision of methods for beneficiating coal:

(1) which are efficient and economical;

(2) which employ parting liquids that can be essentially completelyrecovered at a modest cost;

(3) which employ parting liquids with specific gravities in a range thatmake the liquids capable of effecting a sharp separation between thecoal and associated foreign matter;

(4) which employ parting liquids that are available in large quantitiesat modest cost;

(5) which employ non-corrosive, non-toxic, and non-flammable partingliquids that are chemically inert with respect to coal under the processconditions we employ;

(6) which can be carried out at ambient pressure and temperature orunder conditions which vary only modestly from ambient;

(7) which employ parting liquids that will not leave corrosive or otherunwanted residues on the product coal;

(8) which are efficient even when the moisture content of the coal to beprocessed is high;

(9) which are capable of efficiently recovering coal from slurry ponds,gob piles, and the like at modest cost;

(10) in which the separation of the coal from the foreign materialproceeds rapidly;

(11) which are highly effective in separating sulfur from coal;

(12) which, in conjunction with the preceding object, are capable ofseparating organic as well as pyritic and sulfate sulfur;

(13) which do not have the slime and flocculation problems common tomany gravity separation processes;

(14) in which the specific gravity of the parting liquid can be readilyadjusted and, equally easily, be kept constant or varied in a controlledmanner under changing pressure and temperature conditions;

(15) which are effective to separate coal of large size consists and ofvery small particle size;

(16) which do not generate ecologically undesirable wastes.

Another important and primary object of our invention resides in theprovision of novel, improved methods for transporting coal and othersolids from place-to-place.

Related and important but more specific objects of the invention residein the provision of solids transporting techniques:

(17) which are efficient and economical and in which the solids aretransported in slurry form;

(18) which, in conjunction with the preceding object, permitsubstantially all of the carrier liquid to be recovered from the solidsat the terminus with only modest expenditures of energy;

(19) in which, in conjunction with the preceding object, anon-corrosive, non-toxic, and non-flammable fluorochloro derivative of alower alkyl which has a low viscosity, which is easily recovered, andwhich is chemically inert relative to the solids under processconditions or 1,2-difluoroethane is employed as the carrier liquid;

(20) which have the advantage that the carrier liquids do not causeflocculation problems;

(21) which employ a carrier liquid that permits the solids-to-liquidratio of the slurry to be increased above conventional levels without anincrease in the power required to move the slurry;

(22) which minimize the tendency of the particles to pack and thereforepermit flow to be initiated virtually at once even after the slurry hasbeen static for an extended period of time.

Still another primary object of the present invention resides in theprovision of novel, improved techniques for associating additives withcoal and other solids to modify the characteristics of the solidmaterial.

Related and more specific but also important objects reside in theprovision of techniques:

(23) which can be used to distribute any of a variety of additivesuniformly and economically;

(24) which can be employed to advantage to dedust and waterproof coal;

(25) which can be employed to intimately distribute compositions such asquicklime among coal and thereby reduce the sulfur pollutants generatedwhen the coal is burned;

(26) which are capable of introducing additives into even fine pores andmicro cracks in the solids being treated;

(27) in which the additive is associated with the solids by dispersingit in 1,2-difluoroethane or a liquid, fluorochloro derivative of methaneor ethane; spraying the resulting composition on the solids orsubmerging the solids in or drenching them with the composition; andremoving the liquid carrier;

(28) in which, in conjunction with the preceding object, the carrierliquid is one which is non-corrosive, non-flammable, non-toxic,chemically inert with respect to the additive and the solids, andreadily recovered from the solids;

(29) which can be carried out under ambient or other mild conditions andwithout expensive and exotic process equipment;

(30) which can employ as carrier liquids those used in accord with theprinciples of the present invention in the beneficiation andtransportation of coal, thereby simplifying and reducing the cost ofmulti-step processing of coal;

(31) which avoid the introduction of water into the product, therebyavoiding the deleterious effects which water can have;

(32) which can be employed to associate a binder with coal so that thecoal can subsequently and economically be agglomerated into structurallystable briquettes and the like.

An associated, primary object of our invention resides in the provisionof novel, improved methods for economically making briquettes fromparticulate coal in which a binder is associated with the coal bydispersing it thereon in a 1,2-difluoroethane or liquidfluorochlorocarbon carrier and in which the carrier is then removed andthe particles compacted into the desired shape.

A further important and primary object of our invention resides in theprovision of novel, improved, integrated methods for processing raw coaland for conveying it from a mine face to a location where the productcoal is to be burned, processed, shipped, or otherwise used.

Related and more specific but nevertheless important objects of theinvention reside in the provision of such coal handling and processingtechniques;

(33) which optimize the recovery of raw coal and its conversion into aproduct of maximum usefulness as well as the movement of the raw coal toa point-of-use or other terminus;

(34) which are capable of producing higher yields than can be gained bypresent commercial techniques;

(35) in which the handling and processing steps are so related as tomaximize the efficiency of the process;

(36) which reduce the manpower required to mine and process coal and theattendant problems and expense;

(37) which, to a substantial extent, insulate the mining, processing,and transportation of coal from the effects of inclement weather andadverse climates;

(38) which reduce the handling of foreign material associated with thecoal;

(39) in which the coal can be protected against oxidation until itreaches the point of consumption;

(40) which can also be employed to efficiently dispose of the refusegenerated in the consumption of the coal;

(41) which promote safety and productivity and extend the useful servicelife of equipment;

(42) which can be utilized to reduce the sulfur generated in thecombustion of coal;

(43) which can be used to generate refuse piles with less potential forecological damage than is currently the case;

(44) which employ conveyor apparatus that is less bulky and more easilyrelocated than that of conventional character.

Yet another primary object of our invention resides in the provision ofnovel, improved techniques for recovering the fluorochlorocarbons and1,2-difluoroethane employed in our novel cleaning, transporting,additive incorporating, and briquetting processes and in our novel,integrated process for handling and processing coal from the mine faceto the point-of-use or other terminus.

Important, related, and more specific objects of the invention reside inthe provision of processes in accord with the preceding object:

(45) by which essentially quantitative amounts of thefluorochlorocarbons and 1,2-difluoroethane can be recovered at aneconomic cost;

(46) which can readily be integrated with the process in which the1,2-difluoroethane or fluorochlorocarbon is employed.

Still another important and primary object of the invention resides inthe provision of novel, improved apparatuses in and by which the variousprocesses discussed above can be carried out.

Other important objects and features and additional advantages of ourinvention will be apparent to those knowledgeable in the relevant artsfrom the foregoing and from the appended claims and working examples andfrom the detailed description and discussion which follows taken inconjunction with the accompanying drawing, in which:

FIG. 1 is a schematic illustration of apparatus for beneficiating orcleaning coal in accord with the principles of the present invention andfor recovering from the coal and the foreign material separatedtherefrom 1,2-difluoroethane or a fluorochlorocarbon employed as aparting liquid in the beneficiation process;

FIG. 2 is a schematic illustration of one type of apparatus forcontrolling and adjusting the specific gravity of the parting liquidemployed in the beneficiation apparatus of FIG. 1;

FIG. 3 is a schematic illustration of a second form of apparatus forcontrolling and adjusting the specific gravity of the parting liquid;

FIG. 4 is a view similar to FIG. 1 of coal beneficiation apparatus inaccord with the principles of our invention which is designed for theconservation of heat energy;

FIG. 5 is a view similar to FIG. 4 of a second form of coalbeneficiation apparatus designed for the conservation of heat energy;

FIGS. 6 and 7 are schematic illustrations of alternate systems forrecovering 1,2-difluoroethane and fluorochlorocarbons; these systems canbe used to recover 1,2-difluoroethane and fluorochlorocarbons used asparting liquids in beneficiation processes, as carrier liquids, etc. inother applications of our invention, and for various purposes in otherprocesses;

FIG. 8 is a schematic illustration of an integrated system in accordwith the principles of the present invention for handling and processingraw coal;

FIG. 9 is a schematic illustration of a final cleaning plant employed inthe integrated system of FIG. 8;

FIG. 10 is a schematic illustration of apparatus for associatingadditives with coal in accord with the principles of the presentinvention; and

FIG. 11 is a schematic illustration of a pilot scale plant forbeneficiating coal in accord with the principles of the presentinvention.

Referring now to the drawing, FIG. 1 schematically depicts a plant orsystem 20 for cleaning coal which is constructed in accord with theprinciples of the present invention. The major components of system 20include a conditioning tank or conditioner 22 which can be omitted inthose applications where conditioning is not required. The run-of-mineor other raw coal to be cleaned is transferred from a storage facilityto the conditioning tank as by screw conveyor 24. The plant alsoincludes: a separator 26 of bath, drum, trough, cyclone or otherconstruction in which gangue or ash is separated from the coal by agravity or centrifugal separation (or sink-float) process; dryers 28 and30 for recovering the parting liquid from the clean coal (or floats) andthe rejects (or sinks); and a system identified generally by referencecharacter 32 for recovering parting liquid in vapor form fromconditioning tank 22, separator 26, and dryers 28 and 30; condensing thevapor to a liquid; and returning the liquid to storage tank 34. Alsoincorporated in the system are a storage facility 36 from which asurface active agent can be introduced into the media supply line totank 22 by pump 38 and a heating system 40 for adjusting the effectivetemperature of the coal in the conditioning tank before it istransferred to separator 26.

The conveyor 24 for feeding the raw coal into the conditioning unit canbe of the screw or auger type. As shown in FIG. 1, it will typically bepositioned with a gap between the discharge end and the surface of theliquid in the conditioner. This keeps vaporized liquid in theconditioner, necessarily under some pressure, from blowing out throughthe conveyor when warm coal is introduced into the conditioner.

Trichlorofluoromethane or another of the fluorochlorocarbon partingliquids we can use or 1,2-difluoroethane is pumped at a controlled rateby pump 41 to the discharge side of pump 38 where it is premixed withthe surface active agent (if employed) to insure subsequent homogeneousdistribution of the latter.

The parting liquid or mixture of this constituent and surface activeagent then flows to conditioning tank 22 where the liquid phase and coalintroduced by conveyor 24 are blended into a uniform mixture by agitator42. The latter also generates the turbulence necessary to insuresufficient surface and thermal exposure of the raw coal to theconditioning material or materials.

At the same time, heating system 40 may be utilized to add to themixture such heat as may be necessary to control the temperature, andtherefore the specific gravity, of the parting liquid in separator 26.Heating system 40 includes a tube type or other circulating liquid heatexchanger 44 in the bottom of conditioning tank 22 and a pump 46 forcirculating steam or hot water from a boiler 48 to and through heatexchanger 44 and back to the boiler.

Only modest quantities of heat will, at most, need to be added to thecoal being cleaned. This is because it is not necessary to heat largerparticles or lumps of coal throughout. It is only required that theirsurface temperature be approximately that of the parting liquid inseparator 26 during the short period of time the coal remains in theseparator.

It is also significant that "hot" coal, for example that in thesummertime, can be cooled in tank 22 without using additional energy tokeep the temperature of the bath in separator 26 from rising iftrichlorofluoromethane or a comparable fluorochlorocarbon is employed asthe parting liquid. Because this compound has a boiling point onlyslightly above room temperature, such coal will cause the parting liquidintroduced into tank 22 by pump 41 to evaporate. The latent heat ofvaporization is supplied by the coal, and the temperature of the coaland other components of the mixture in tank 22 is accordingly reduced asthe parting liquid vaporizes.

The mixture formed in conditioning tank 22 is transferred to separator26 as by a screw type conveyor 50. The coal in the mixture floats to thetop of the body or bath 52 of parting liquid in the separator while theash or rejects sink to the bottom.

The coal is skimmed from the surface of sink-float bath 52 as by anauger conveyor 54, preferably equipped with folding flights. Thisskimmer discharges the coal into the lower, feed end of an upwardlyinclined conveyor 55. The conveyor transfers the coal to floats dryer28. As the coal moves upwardly through transfer conveyor 55, the bulk ofthe parting liquid drains from it and flows by gravity back intoseparator 26.

Rejects are removed from the bottom of separator 26 as by a foldingflight, auger conveyor 56 and discharged into the lower, feed end of asecond, upwardly inclined, transfer conveyor 58 in which the partingliquid drains from the rejects into separator 26. From conveyor 58, therejects are discharged into sinks dryer 30.

Dryers 28 and 30 will typically be of the indirect, conductive type.Examples of such dryers which are suitable are the rotary, steam tube,and Hollow Flite types. Steam or hot water is supplied to the dryers tovaporize the parting liquid associated with the floats and sinks fromboiler 48 by pump 46 through supply conduit system 59. After circulatingthrough the dryers, the heat exchange medium returns to the boilerthrough fluid conduit system 60.

For the sake of clarity, sinks dryer 30 is shown at a lower elevationthan floats dryer 28 in FIG. 1. In actual practice it is located atapproximately the same level as dryer 28 so liquid can drain back intoseparator 26 which it could not do if the dryer were located at theillustrated level.

The dry coal and dry rejects are discharged from dryers 28 and 30 tomaterial handling systems indicated generally by arrows 61 and 62 inFIG. 1. The rejects are transferred to a gob pile and the clean coal tothe point-of-use or to a coking or other coal treating operation.

Vaporized parting liquid generated in dryers 28 and 30 is combined withthat from conditioning tank 22 and separator 26 in a line 63 leading tothe inlet side of a compressor 64. As the vapor from conditioning tank22 may carry a significant amount of entrained fines, this vapor isfirst preferably scrubbed with parting liquid in a conventional scrubber66.

After flowing from the compressor through a valve 67 employed tomaintain pressure in the system, the vaporized parting liquid iscirculated through a condenser 68 which may be of the conventional shelland tube type. Cooling liquid (typically water) at a temperature on theorder of 85° F. is circulated from the lower end of a conventionalcooling tower 72 through the condenser by pump 74 to condense theparting liquid.

After exiting from the condenser, the water, now at a temperature on theorder of 95° F., returns to and is sprayed into the upper end of thecooling tower through nozzles 76. As the water flows down through thecooling tower, it is contacted by an upwardly moving stream of airgenerated by cooling tower fan 78. This reduces its temperature to thelevel at which it is circulated to condenser 68.

Condensed parting liquid flows through an expansion valve or orifice 80to reduce its pressure to atmospheric and then to the parting liquidstorage facility or tank 34.

Noncondensible gases and any parting liquid which may not have condensedproceed from condenser 68 to a purge unit 82. This may be a scrubber orother absorption type device or a mechanically refrigerated unit, forexample. The remaining parting liquid is condensed in this unit andreturned to storage tank 34.

Noncondensible gases flow through a conduit system identified generallyby reference character 84 to the floats and sinks dryers 28 and 30. Thegases are circulated through these dryers in countercurrent relationshipto the solid material to strip parting liquid vapors from the solidmaterial.

In cleaning some coals, significant amounts of middlings may begenerated. To expedite the separation of this material, pump 86 can beemployed. This pump circulates the middlings and parting liquid in whichthey are entrained from a zone in bath 52 intermediate those to whichthe floats and sinks report to a cyclone, centrifuge, or other polishingdevice 88. Here, the solids are separated from the parting liquid anddischarged from the separator as indicated by arrow 90. Depending uponthe proximate analysis of these solids, they are conveyed to either thefloats dryer 28 for clean coal or the sinks dryer 30 for rejects. Theparting liquid is pumped to either conditioning tank 22 as shown bysolid line 92 or to gravity separation tank 26 as shown by dotted arrow94.

As will be apparent to the reader, variations can be made in theillustrated equipment. Obvious changes are necessary if the conditioningtank 22 is not employed. Other types of conveyors may be used. Theconditioner tank and agitator may be replaced with a pug mill, jacketedscrew conveyor, or other blender, etc. Centrifuges can be employedinstead of or in addition to drip drying as in conveyors 55 and 58 toremove parting liquid (ca. 97 percent) from the solids as can static andvibrating screens, etc. And shelf-type and other kinds of dryers can beused instead of those discussed above. Still other alternatives willreadily suggest themselves to those skilled in the relevant arts.

In addition to those discussed above, a system as just described has theadvantage that losses of the parting liquid constituents are acceptable.In a typical operation, losses would not exceed 0.25 pounds of liquidper ton of coal cleaned.

As indicated above and discussed in more detail hereinafter, it may insome instances be advantageous to adjust the specific gravity of theparting liquid to increase the amount of ash separated from the coaleven though this may result in some coal reporting to the sinks andthereby lowering the yield.

The manner in which this is done in the case of the preferred partingliquid, trichlorofluoromethane, is exemplary. Trichlorofluoromethane hasa nominal specific gravity of 1.5 which can readily be varied over arange of approximately 1.4-1.55 by increasing the temperature under anabove-atmospheric pressure to reduce the specific gravity or decreasingthe temperature to increase the specific gravity. One typical system foradjusting the specific gravity of the parting liquid by these techniquesis shown in FIG. 2 and identified by reference character 100.

This system differs from that shown in FIG. 1 in that a thermalconditioner or holding tank 102 is interposed between conditioner 104and separator 106, which can be isolated from the floats and sinksdryers (not shown) by valves 108 and 110.

A coil 112 through which a heat transfer fluid such as hot water, steam,etc. can be circulated is housed in thermal conditioner tank 102. Theconditioner tank is connected to the suction side of a compressor 114.

In operation, the slurry of coal and parting liquid formed inconditioner 104 is transferred to thermal conditioner 102 by pump 116.Here, the specific gravity of the parting liquid can be raised byemploying compressor 114 to flash liquid in the conditioner into vapor,extracting heat from and increasing the specific gravity of theremaining liquid. Alternatively, the specific gravity of the partingliquid can be lowered by adding heat to the liquid with heater 112. Thiscan typically be accomplished in not more than 10 minutes.

The practical limits within which the specific gravity of the partingliquid can be decreased and increased will vary depending upon theparting liquid. The limits will be comparable to those mentioned abovefor trichlorofluoromethane.

The flow of heat transfer fluid and therefore the amount of heat addedto the coal and parting liquid can be controlled manually. Or, as shown,the flow can be regulated by a conventional thermostatic valve 118having a senser 120 in the thermal conditioning tank.

Similarly, evacuation of parting liquid vapor from thermal conditioner102 to decrease the specific gravity of the parting liquid can also becontrolled manually or automatically. In the latter mode control isexercised by a valve 122 with a temperature responsive senser 124 in thethermal conditioner tank.

If reduced pressure is employed to alter the specific gravity of theparting liquid, valves 108 and 110 will be kept closed until theseparation step is completed. This, together with the seal afforded bypump 116, isolates the thermal conditioner and gravity separator fromthe ambient atmosphere, insuring that the pressure on the parting liquidand its specific gravity remain constant.

We pointed out above that larger changes in the specific gravity of theparting liquid can readily be made by diluting the fluorochlorocarbon or1,2-difluoroethane with a light petroleum fraction or a liquidhydrocarbon. A coal cleaning system in which the specific gravity of theparting liquid can be altered in this fashion is illustrated in FIG. 3and identified by reference character 130.

System 130 is comparable to system 20 in that it includes a conditionertank 132; a separator 134; floats and sinks dryers 136 and 138; acondenser 140 to which recovered vapors are pumped by compressor 141; apurge unit 142 for recovering parting liquid from the dryers, purging itof noncondensibles, and condensing it; and a fluorochlorocarbon storagetank 144 which may be used to contain 1,2-difluoroethane. System 130also includes a storage tank 146 for the liquid diluent employed tolower the specific gravity of the fluorochlorocarbon or1,2-difluoroethane and a storage tank 148 for the partingliquid--typically a mixture of trichlorofluoromethane and petroleumether.

The operation of this system is generally the same as that shown inFIG. 1. The recovered, condensed parting liquid, however, can bereturned from condenser 140 to the parting liquid storage tank 148and/or stripped of noncondensibles in purge unit 142 and circulated to aconventional fractionation tower 149.

Parting liquid is transferred from tank 148 to conditioning tank 132 bypump 150 as necessary to maintain the level of parting liquid in gravityseparation tank 134 constant. This level can be automatically maintainedby a modulating valve 152 in the parting liquid supply line 154. Theoperation of this valve is regulated by a conventional level controller156 having a senser (not shown) in tank 134.

The parting liquid returned to fractionation tower 149 is first passedthrough an evaporator 157 to insure that it is in the gas phase. Thegases are then separated in the fractionation tower into1,2-difluoroethane fluorochlorocarbon and diluent constituents which,after condensing, return to tanks 144 and 146, respectively. Liquids arefed from these tanks into parting liquid supply line 154 as necessary tokeep the density of the parting liquid constant. Control over thisoperation is afforded by modulating valves 158 and 160 in supply lines162 and 164. The operation of the valves is regulated by a conventionaldensity controller 165 with a senser (not shown) in gravity separationtank 134.

If the supply of liquids in tanks 144 and 146 runs low, valve 166 isopened. Liquid is then pumped from tank 148 to evaporator 157 andfractionation tower 149 to replenish the supply. Conversely, if thelevels in the fluorochlorocarbon and diluent tanks become too high,valve 167 can be closed and the 1,2-difluoroethane orfluorochlorocarbon, diluent mixture returned directly to storagefacility 148 from purge unit 142 through line 168.

A third valve, 169, reduces the pressure on the liquid returned tostorage tank 148 through line 170a from that in the condenser (thedischarge pressure of compressor 141) to that in the storage tank. Line170b is used to return vapors generated by the expansion of liquid invalve 169 to the inlet side of compressor 141.

A typical parting liquid specific gravity that the system just describedmight be employed to maintain is 1.3. This can be generated at ambienttemperature and pressure by mixing 22.2 weight percent petroleum etherwith 77.8 percent trichlorofluoromethane.

As the seasons change, the temperature of the incoming coal may vary.The variations in the specific gravity of the parting liquid which thiswill tend to cause are automatically compensated for in the system shownin FIG. 3. Density controller 165 will vary the proportions oftrichlorofluoromethane and diluent to offset any tendency of thespecific gravity to vary.

As discussed above, coal cleaning plants in accord with the principlesof the present invention may also be constructed in a manner which willpermit significant amounts of heat generated in the course of cleaningthe coal to be recovered. One arrangement for accomplishing this goal isshown in FIG. 4 and identified by reference character 171. In thissystem, vaporized parting liquid is pumped to a condenser 172 asdescribed above by compressor 173. Here, it gives up heat to a coolingliquid circulated through the condenser, increasing the temperature ofthe latter and condensing the parting liquid.

The heated cooling water is discharged from condenser 172 at atemperature typically in the range of 95° to 120° F., which is wellabove the vaporization temperature of our preferredtrichlorofluoromethane. The heated water is circulated by pump 174through conduit system 176 to floats and sinks dryers 178 and 180 andthen through conduit system 182 back to the condenser, thereby supplyingheat required to operate the dryers. This further reduces the alreadymodest cost of cleaning coal in accord with the principles of thepresent invention.

In some applications, the water discharged from condenser 172 maycontain more heat than is needed for the operation of dryers 178 and180. A three-way modulating valve 184 controlled by a thermostat 186 istherefore preferably interposed between pump 174 and dryers 178 and 180.This valve automatically diverts water as necessary to cooling tower 188where its temperature is reduced. The cool water is piped throughconduit 190 and mixed with the water recirculated to condenser 172 fromthe dryers.

Alternatively, or in addition, the excess hot water can simply bedischarged from the system into a sewer, etc. as shown by line 192 andreplaced by cooler makeup water as shown by arrow 194.

FIG. 5 illustrates a heat conservation arrangement 200 which differsfrom system 171 in that the vaporized parting liquid recovered from thefloats and sinks dryers, gravity separation tank, and conditioning tank(the conditioning tank and separator are not shown) is employed tooperate the dryers.

In system 200, a thermostatically controlled, three-way valve 202 isinterposed between compressor 204 and condenser 206. Vapor recoveredfrom the system components mentioned in the preceding paragraph flowsfrom this valve to floats and sinks dryers 208 and 210 through conduits212 and 214 to operate the dryers. Vapor in excess of that required tooperate the dryers is automatically diverted to condenser 206 where itis processed as described above.

Parting liquid condensed in the dryers returns to the storage facilitythrough conduits identified generally by reference character 216.Noncondensibles and vapor flow through conduits identified collectivelyby reference character 218 to condenser 206 where the parting liquid iscondensed and returned to storage. Noncondensibles and any remaininguncondensed parting liquid flow to a purge unit (not shown) such as thatidentified by reference character 82 in FIG. 1. Here, additional partingliquid is recovered and returned to storage. Noncondensibles arerecirculated to the dryers 208 and 210 as a stripping gas or rejectedfrom the system.

The system just described has the virtue of reducing the capacity ofcondenser 206 with a concomitant decrease in capital investment and inthe cost of operating the coal cleaning plant.

As shown in the drawing, plants 171 and 200 are both preferably equippedwith a second, independent heat source such as the boiler 48 andcirculation system 59, 60 illustrated in FIG. 1. This system is usedduring start-up of the plant when required and, if necessary, to augmentthe heat supplied to the floats and sinks dryers 178 and 180 or 208 and210 by the heated fluid in plant 171 or the vaporized parting liquid inplant 200.

One system for drying the coal and the rejects and recovering thevaporized parting liquid associated with the solids is illustrated inFIG. 1 and was described above. A second system for accomplishing theseobjectives is illustrated in FIG. 6 and identified by referencecharacter 220.

In this system the drip dried but vapor saturated coal or refuse is fedinto one end of a purge tube or vessel 222 through which it is conveyedas with auger type conveyor 224. As the material moves through purgetube 222, the vaporized parting liquid is stripped from it by gasesintroduced at the discharge end of the purge tube. These gases arecirculated through the purge tube in countercurrent relationship to themovement of the solids by compressor 226 and exit from the feed end ofthe purge tube.

Entrained solids are removed from the vapor laden gases exiting from thepurge tube by a filter 228. The pressure on the mixture is thenincreased by compressor 226 to a level at which the parting liquid canbe economically condensed; and the mixture is circulated to condenser230, which may be of the character described above. The parting liquidvapor is condensed and the liquid returned to storage.

Heat rejected from the condenser may be recovered as discussed above inconjunction with the systems 171 and 200 shown in FIGS. 4 and 5.

The noncondensible gases rejected from the condenser are recirculated topurge tube 222 for use as a stripping gas. As shown in FIG. 6, they mayfirst, however, be compressed to a higher pressure and circulatedthrough a second condenser to recover additional parting liquid (thesecondary compressor and condenser are identified collectively byreference character 232).

In addition, or optionally, outside air can be introduced into thedischarge end of purge tube 222 to strip vapors from the solids thereinas indicated by arrow 234.

Other vapor recovered from the coal cleaning plant can also be strippedof noncondensibles recovered in system 220. The gases are introducedinto the parting liquid recovery system at the location indicated byarrow 236.

The components of a parting liquid recovery system of the character justdescribed do not necessarily have to be as shown in FIG. 6. For example,a belt conveyor should be substituted for the illustrated screwconveyor. A vertical purge tube could be employed and the conveyoreliminated, the solids travelling down the purge tube by gravity. Stillother modifications will suggest themselves to those conversant with therelevant arts.

In yet another variation of the illustrated system, the gases and vaporsare evacuated by drawing a vacuum in the purge tube. The parting liquidis then recovered and the noncondensible gases utilized as discussedabove or rejected to the ambient surroundings as they also can be in theillustrated system.

While the system for recovering the parting liquid described in thepreceding paragraph is somewhat complicated and cumbersome because ofthe locks, etc. needed to maintain a subatmospheric pressure in thepurge vessel, it is also efficient. For example, a typical coal contains42.76 percent by volume voids. At 75° F., this coal contains 6.28 poundsof trichlorofluoromethane per ton. By reducing the pressure on the driedcoal to 29 inches of Hg below atmospheric and recovering the gasesgenerated in doing so, all but 0.24 pounds per ton of the parting liquidcan be recovered.

We have also discovered that the natural affinity which1,2-difluoroethane and the fluorochlorocarbons we employ possess foroils can be taken advantage of in recovering vaporized parting liquid.The vapor is contacted with oil, which absorbs the vaporized partingliquid but not the noncondensibles, which can be used as a stripping gasor rejected. The oil is then heated to release the parting liquid whichis condensed and recycled. This approach is both more effective and moreeconomical than the previously described mechanical compression andcondensation when the ratio of noncondensible gases to parting liquidvapor is high.

An exemplary system for recovering parting liquid by the technique justdiscussed is illustrated in FIG. 7 and identified by reference character240.

In this system, the vaporized parting liquid is stripped from the coalor refuse in purge tube 242, compressed, and pumped into the lower endof vertical tower 244 by compressor 246. Number 2 fuel oil or otherabsorbent liquid is sprayed into the upper end of tower 244 throughnozzles 248 and travels downwardly through the tower in countercurrentrelationship to the upwardly flowing gases. The absorption medium scrubsor strips the parting liquid vapors from the noncondensible gases, thevapor rich oil collecting in a sump 250 at the bottom of tower 244.Noncondensible gases pass through a separator 251, which removesentrained liquid and vapors; exit from the upper end of the tower; andrecirculate to purge tube 242.

The parting liquid is recovered by pumping the 1,2-difluoroethane orfluorochlorocarbon rich oil from sump 250 through a heater or heatexchanger 252 with pump 254. The parting liquid vapor released from theoil in heater 252 is condensed as described previously (the condenser isnot shown) and recirculated to the coal cleaning process or returned tostorage.

The stripped absorption medium is cooled in a heat exchanger 256 toincrease its absorption capacity and recirculated through tower 244.

The heaters or heat exchangers 252 and 256 may be of the shell and tubetype although it is not essential that this particular kind of device beused.

As shown in FIG. 7, oil pumped from sump 250 may be diverted into line258 and sprayed into tower 244 through nozzles 260. This increases theconcentration of parting liquid in the oil collecting in sump 250,reducing the thermal loads on heat exchangers 252 and 256.

System 240 is also designed to recover parting liquid vapors frommixtures collected from other components of the coal cleaning plant suchas the conditioner, gravity separator, and dryers. Gases and vapors fromthese components are circulated through a filter 262, compressed, andcirculated to a condenser 264 by a compressor 266. The parting liquid iscondensed in condenser 264 and recirculated or returned to storage. Thenoncondensible gases rejected from the condenser are combined with thoserecovered from purge unit 242 on the discharge side of compressor 246and thereby recirculated to tower 244 to recover additional partingliquid.

As shown in FIG. 7, an economizer 268 can be interposed between pump 254and heater 252. Pump 269 circulates water or other heat exchange liquidfrom cooler 256 through the economizer. Sensible heat extracted from theoil in cooler 256 by the heat exchange liquid is given up to the partingliquid rich oil flowing to heater 252, thereby conserving energy byreducing the load on the heater.

Also, compressor 246 may be eliminated; and the gases from purge tube242 may be delivered through duct 270 to the inlet of filter 262.

In some applications a combination of the systems 220 and 240 justdiscussed can be used to optimize the recovery of the parting liquid.Mechanical compression and condensation are employed to recover theparting liquid from the vapor rich gases, and the parting liquid isrecovered from the leaner gases by the absorption technique.

It is also to be understood that the purge tubes employed in the systemsof FIGS. 6 and 7 can be used as dryers in the systems described aboveand hereinafter. Or, what is referred to in the description of suchsystems as a dryer may constitute one or more purge tubes and otherdrying equipment arranged in the order deemed most suitable for aparticular application.

As discussed briefly above, coal cleaning apparatus of the characterdescribed in conjunction with FIGS. 1-7 can be integrated into a novelsystem for handling and processing coal in which the parting liquid isalso employed to convey the coal and ash generated in its combustion.One integrated coal handling system of this character is illustrated inFIG. 8 and identified by reference character 271.

In this system, coal is separated from mine face 272 as by a continuousminor or auger 274 such as a Badger Manufacturing Company Coal Badger ora Salem Tool Company MC MUL-T, for example. From the miner the coal andgangue flows to an optional crusher 276, where the mined coal is reducedto a typical top size of in the range of 1.5 inches, and then to aslurry pump 278, where it is mixed with 1,2-difluoroethane or one of thefluorochlorocarbons described above. As shown in FIG. 8, the miner,crusher, and slurry pump can conveniently be mounted on a single chasis280.

The liquid content of the foregoing and other slurries formed in accordwith the principles of the present invention will vary fromapplication-to-application. This phase will, however, constitute from 40to 99 weight percent based on the total weight of the slurry.

Slurry pump 278 transfers the coal and 1,2-difluoroethane orfluorochlorocarbon mixture to a primary cleaning station 282 of thecharacter described above in conjunction with FIGS. 1-6 and preferablylocated in the mine. The dried rejects from the cleaning operation,typically first coated with a dust suppressant, are conveyed to anddumped in a mined-out area of the mine as indicated by arrow 284.

The floats generated in the primary cleaning station (coal plus foreignmaterial not removed in the primary cleaning step) and parting liquidfrom the primary cleaning station form a slurry which is pumped byslurry pump 286 to a final cleaning plant 288 located on the surface.

The initial unit 290 of the final cleaning station, shown in FIG. 9,will typically include a second crusher for reducing the solids in theslurry to the size consist specified by the consumer or to a size whichwill free additional pyrites and/or other foreign material. Unit 290will in general also include a conditioning tank such as that shown inFIG. 1 so that additives and parting liquid can be blended with theslurry, the temperature of the coal adjusted, etc.

From this unit, the slurry is transferred as by screw conveyor 292 to agravity separator 294 also as described above. The sinks from thegravity separator are transferred to a dryer 296 where the1,2-difluoroethane or fluorochlorocarbon parting and carrier liquid isseparated by adding heat to the slurry to evaporate the liquid and bypurging the 1,2-difluoroethane or solids to recover thefluorochlorocarbon from the pores of the solids. Also, as discussedabove, the sinks may first be drip dried to reduce the energy requiredto remove the fluorochlorocarbon or 1,2-difluoroethane by evaporation.Suitable equipment for these functions is that discussed above andillustrated in FIGS. 1, 6, and 7, for example.

The dried rejects, first optionally coated to inhibit oxidation and thegeneration of acidic ground water, are conveyed to a gob pile or otherdisposal area. The vaporized parting liquid recovered from dryer 296,together with that from unit 290 and gravity separation tank 294, flowsto compressor 298. Compressor 298 pumps the vapor to a unit 300typically consisting of a condenser and purge unit as discussed above.

The noncondensibles are separated from the parting liquid vapor in unit300. As in the embodiments of the invention discussed above, they can berecirculated and used as a stripping gas in sinks dryer 296.Alternatively, or in addition, they can first be processed through anabsorber or other conventional device 301 to separate and recovercommercially valuable products such as methane removed from the mineface, etc.

The condensed parting liquid is circulated through conduits identifiedgenerally by reference characters 302, 304, and 306 to slurry pump 278and to mine face 272. The latter liquid along, or with such additives asmay be desired, is sprayed onto the mine face as through nozzles 308.This suppresses dust generated at the mine face, reducing the explosionhazard. The liquid also reduces cutter wear and the power needed tooperate continuous miner 274.

In a typical application the clean coal from gravity separator 294 ispumped in slurry with the parting liquid to a storage tank 310 by slurrypump 312. The slurry is typically stored at ambient temperature andpressure.

On demand, the slurry is withdrawn from storage tank 310 and transferredto a final preparation station 313. This station includes a floats dryerand a parting liquid recovery unit as described above for recovering thefluorochlorocarbon or 1,2-difluoroethane carrier liquid used in thetransport of the coal and for recirculating the noncondensibles to thedryer and/or recovering certain of the gases. Also, the finalpreparation unit may include one or more units for further treating thecoal. For example, quicklime or calcined dolomite can be blended withthe coal at this station to, as discussed above, decrease the sulfurcontent of the combustion products generated when the coal is burned.

The amount of quicklime or dolomite added to the coal will of coursedepend upon a number of factors including the sulfur content of thecoal, the conditions under which it is burned, etc.

In a typical application 90 pounds per ton of 200 m ×0 calcined dolomiteis intimately dispersed on Pittsburgh coal using trichlorofluoromethaneas the carrier. The efficiency of the reaction between the calcium andmagnesium oxides and the sulfur in the coal during the subsequentburning of the coal is ca. 80 percent. This reduces the sulfur contentof the combustion gases from the three percent level of untreated coalto a level of 0.6 percent. The latter level is well within EnvironmentalProtection Agency limits.

The reduction in sulfur content is also well below that which can beachieved by adding the same materials to coal in the conventionalmanner; viz., dry mixing. This technique is capable of only imperfectlydistributing the additive, making the efficiency of the subsequentoxide, sulfur reaction much lower than it is when the additive isdistributed by our novel process.

Our novel process for reducing combustion gas sulfur content is alsosuperior to more conventional techniques for accomplishing the same goalsuch as scrubbing the combustion products. Treating the coal in theexemplary application described above by our process costs ca. $1.13 perton. To accomplish similar results by scrubbing would cost $3-4 per tonof coal burned.

Referring again to FIG. 8, in the exemplary illustrated system the coalis transferred from final preparation station 313 to a boiler 314typically equipped with a precipitator 316 to recover fly ash generatedin the combustion of the coal.

The ash generated in boiler 314 and in precipitator 316, respectively,is quenched in units 318 and 320 to reduce its temperature to on theorder of 100° F. Liquid recovered in final preparation unit 313 iscirculated to the discharge sides of the quench units by pump 322 andmixed with the ash to form a slurry. This slurry is pumped to the sinks(ash) dryer and purge unit 296 of final cleaning plant 288 through aconduit system indicated generally by reference character 324. The ashcan accordingly be dried and disposed of with the rejects from the finalcleaning process.

One important advantage of the novel system 271 just described is thatas much as 10 to 30 percent of the mined solids may not have to beconveyed to the surface, resulting in a significant cost savings. Also,because the rejects from the final cleaning station typically constituteonly 12 to 50 percent of the mined material, the aboveground cost ofdisposing of rejects can also be lowered.

Furthermore, the system is highly versatile. As discussed previously, itcan with only readily made modifications be used to furnish the feed fora coal gasification plant, coking operation, etc. Also, final cleaningplant 288, storage tank 310, and final preparation plant 313 are sourcesof clean coal for shipment to other locations. That is, the user neednot be located at the mine as in the illustrated system.

In addition, as previously mentioned, the system can contain and collectgases such as methane released during mining of the coal. It cansimilarly accommodate gases generated or released during cleaning,transportation, or storage of the coal and/or handling of the ash.

As discussed above, one aspect of our invention has to do with theblending of additives with coal and other solids. Many mechanicalarrangements can be employed for this purpose. In general all that isrequired is an agitator in a vessel to which the solids, the additive,and the 1,2-difluoroethane or fluorochlorocarbon liquid carrier can besupplied or a conventional screw conveyor, rotary mixer, pug mill, etc.

In this rudimentary system the solids, additive, and carrier are mixeduntil the additive is uniformly dispersed. The carrier is thenevaporated into the ambient surroundings, a step which can beaccelerated by supplying heat to the vessel.

FIG. 10 depicts a more sophisticated system 330. This system providesfor recovery of the 1,2-difluoroethane or fluorochlorocarbon and can bereadily incorporated into coal cleaning plants as described above andintegrated systems as shown in FIGS. 8 and 9.

In system 330 distribution of the additive is accomplished in a unit 332which, as described above, may be an agitator equipped vessel, screwconveyor, etc. If system 330 is associated with a coal cleaning plant orintegrated system, the floats dryer can be bypassed and the drip driedfloats transferred directly from the gravity separation operation tounit 332 as indicated by arrow 334. The 1,2-difluoroethane orfluorochlorocarbon carrier and additive are added directly to the unitas indicated by arrows 336 and 338. Alternatively, as shown by arrow340, the additive and liquid can be premixed and then supplied to unit332 as indicated by arrow 336.

The blended product is transferred as indicated by arrow 342 to a dryerof the character discussed above to remove the carrier liquid. Thisliquid is then recovered by any of the techniques described herein andrecirculated, and the noncondensibles stripped from the carrier arerejected or recirculated to the dryer.

The additive can also be added to the conditioning tank or even thegravity separator in those applications of our invention involving acoal cleaning step. Dust suppressants, oxidation inhibitors, and otheradditives can conveniently be added to the clean coal and/or the rejectsby this technique.

Referring again to the drawing, we have described hereinafter a varietyof tests successfully conducted on a pilot plant scale. The plant inwhich these tests were made is shown diagrammatically in FIG. 11 andidentified by reference character 350.

The pilot plant includes a storage tank 352 for the parting liquid. Thetank can be connected to the inlet side of pump 354 by opening valves356 and 358. With valves 359 and 360 also open and valve 362 closed,pump 354 pumps the liquid through a filter 364 into a 24 inch diameterby 6 foot long gravity separation vessel 366 until the vessel is filledto the level indicated by reference character 368. A valve 369 is openedwhile tank 366 is filled to equalize the pressure in storage tank 352with that elsewhere in the system so that a vacuum will not be drawn inthe tank.

After tank 366 is filled, valves 358, 359, and 360 are closed; and valve362 is opened. This valve drains a second, similarly oriented anddimensioned vessel 370 in which clean coal is first drip dried and thendried with a heated gas.

If the coal is conditioned prior to the separation step1,2-difluoroethane or, fluorochlorocarbon parting liquid or the liquidplus a surface active agent and any other additives are mixed with thecoal by hand in a drum. The coal, conditioned or not, is placed in ahopper 371 and transferred through a valve 372 into a hand-cranked screwconveyor 374. The screw conveyor discharges the coal into the bath 376of parting liquid.

As the separation of the coal and rejects proceeds, the floats areskimmed from the body 376 of parting liquid and transferred to dryingvessel 370 by a motor driven screw conveyor 380.

Valves 362, 382, 383, and 356 are open, and pump 354 is energized asthis occurs. The parting liquid draining from vessel 370 is accordinglypumped through filter 384 back into storage tank 352. At the end of theseparation step the drain valve 360 from gravity separation vessel 366is also opened and the liquid in it drained and pumped through filter364 to storage tank 352.

The solids in tanks 366 (sinks) and 370 (floats) are trapped on 140 meshscreens 385 and 386 in the bottoms of tanks 366 and 370, respectively.Filters 364 and 384 trap three micron and larger particles which passthrough the screens.

Valves 387 and 388 are open throughout the coal separation process.Saturated parting liquid vapor flows through these valves to a shell andtube condenser 390 and is condensed, using water as a cooling liquid.The condensed liquid is pumped to storage tank 352 through valves 392and 356 by pump 354.

After the parting liquid has drained from tanks 366 and 370, a Rootsblower 394 is energized; and hot water (ca. 140° F.) is circulatedthrough the shell side of a shell and tube type heat exchanger 396.Parting liquid vapor is first circulated through the tube side of heatexchanger 396 by the blower to superheat it and then through filters 364and 384 and through the solids in tanks 366 and 370 to dry the solidstrapped on screens 385 and 386 and on the filters.

Noncondensibles and any vapor which is not condensed in condenser 390are compressed by a diaphragm compressor 398 and pumped to a pipelinecondenser 400. Here, the remaining parting liquid is condensed. Thenoncondensibles are rejected to the surrounding environment through avalve 402 provided to maintain pressure in the system. The condensateflows through a float valve 404, provided for the same purpose, and isreturned to storage tank 352.

After the solids have been dried the bottoms of tanks or vessels 366 and370 are opened and screens 385 and 386 removed, discharging the coal andrejects into separate receptacles (not shown). Filters 384 and 364 areremoved. The coal trapped on filter 384 is combined with the coal fromdrip dry tank 370, and the rejects trapped on filter 364 are combinedwith those from gravity separation vessel 366. The solids are weighedand subjected to proximate analyses, etc. in accord with the testprocedures set forth below.

Pilot plant 350 also demonstrates that coal can be readily transportedin a slurry as discussed above. The coal is moved in this manner fromseparator 366 to drip dry tank 370.

The examples which follow describe representative tests which illustratevarious facets of our novel coal cleaning and other processes.

For the sake of convenience the bulk of these tests were made on a benchscale basis.

In the bench tests a raw coal sample is quartered as prescribed by ASTMStandard No. D2013-72 into two or more kilogram lots. One lot isemployed to characterize the raw coal as to size consist and bulk watercontent and for a complete proximate analysis which furnishes a standardfor comparison.

The samples are stored in airtight containers until tested.

At the time of the bench test, the coal is, in some cases, first mixedwith the parting liquid or the latter plus a surface active agent for2-30 seconds to form a slurry containing 50-80 percent solids.

Separation is effected in one liter of the selected parting liquid in asix-inch diameter container at room temperature (65°-72° F.). The coalis transferred to the container in batches of 25-50 grams and brieflystirred.

The clean coal and the rejects are recovered separately from the partingliquid which is then filtered to recover any middlings which may bepresent (the "middlings" are those fragments which do not report to thesinks or the floats usually because they are very small in size and ofalmost the same specific gravity as the parting liquid).

The three phases are separately air dried. A material balance is made,and proximate analyses are made of the coal or the coal and themiddlings.

If the water content of the coal is desired, that phase is not dried. Itis instead placed in a flask and heated at a temperature of 30° C. untilthe parting liquid is completely evaporated. The sample is then weighed,heated at 100° C. in a vacuum oven until the free water evaporates, andreweighed. The difference is the weight of the water content.

Variations in the basis bench test procedure just described will bediscussed in the examples in which they are introduced.

To more nearly duplicate a commercial operation, tests are also run inthe pilot plant 350 described above. Samples of up to about 1,000 poundsare employed; and the cleaning rate is six-eight tons per hour.

Any surface active agents which are to be employed are first mixed withthe parting liquid. The coal is then added on an approximately equalweight basis, forming a stiff, moist mixture. This mixture is batchedinto the pilot plant feed hopper 371 described above.

Dried coal recovered from the pilot plant is quartered in accord withASTM Standard D2013-72, providing samples for proximate and otheranalyses.

The tables which are included in the examples are for the most partself-explanatory. However, the significance of two entries may not bereadily apparent. These are "BTU Yield" and "percent reduction permillion BTU's".

BTU Yield is determined by the formula: ##EQU1## BTU Yield shows whatpercent of a run-of-mine coal's heating value can be sold at theanalysis constituted by the figures in a given column in the tableswhich follow.

Taken with the figures indicative of reduction in sulfur and ash contentand the amount of coal reporting to the sinks, BTU Yield is indicativeof the effectiveness of the coal cleaning process.

If the BTU Yield is low, the other figures will show whether this isattributable to the removal of pyritic sulfur and/or dissolved organicmaterial to the refuse (desirable) or whether the coal is beingmisplaced to the rejects (undesirable).

Conversely, if the BTU Yield is high, the sulfur and ash reductionfigures will show whether this is attributable to the lack of pyritesand/or dissolved organic material in the rejects or to the efficiency ofthe operation in separating foreign matter from the raw coal.

In both cases the BTU Yield is valuable because it is a direct indicatorof the per BTU cost of mining and recovering the coal. Coupled withsulfur and ash reduction, it is also indicative of the cost of handlingrefuse from the combustion process and of maintaining the sulfur levelin the combustion products at an acceptable level.

Percent reduction per million BTUs can be calculated for ash and fortotal, pyritic, and organic sulfur. The figure is calculated by theformula: ##EQU2## where y is pounds of ash, sulfur, etc. in the cleancoal and z is the same for the raw or uncleaned coal. Percent reduction/10⁶ BTU is a significant value because it relates ash and sulfurcontent to product BTU; and BTUs or fixed carbon, not pounds, are whatis of value to the customer.

In the results reported in the examples all percentages are by weightunless otherwise indicated. All quantitative results are reported on amoisture-free basis.

Complete proximate analyses are not made in all cases, and this isreflected in the data tabulated in the examples. Such analyses areexpensive and time consuming; and it is not necessary to make a completeanalysis of the coal from each and every run because reduction in ashcontent, standing alone, is a good measure of the efficiency of a coalcleaning process.

EXAMPLE I

To demonstrate the effectiveness of our novel process in its most basicor elementary form, a bench scale test as described above was run at aspecific gravity of 1.50 on Upper Freeport coal having a size consist of3/8 inch ×0 and a moisture content of 6.5 percent (nominal). The sizedistribution of the particles in the same was as follows:

    ______________________________________                                        +3/8 inch           7.5    percent                                            3/8 × 5m      27.7   percent                                            5m × 10m      21.7   percent                                            10m × 30m     29.9   percent                                            30m × 60m     10.8   percent                                            60m × 100m    1.6    percent                                            -100m               1      percent                                            ______________________________________                                    

Trichlorofluoromethane (CCl₃ F) without additives was used as theparting liquid.

The ash content of the coal was reduced from 35.37 to 13.10 percent inthe test, showing that a major part of the foreign matter had beenseparated from the coal. More ash could have been removed by reducingthe size of the larger particles. They were sufficiently large that allof the ash had not been liberated from the coal itself.

The test is also significant in that the coal which was used had amoisture content much higher than that which is acceptable if the coalis to be cleaned by processes such as described in the Tveter patentidentified above.

EXAMPLE II

To demonstrate that fluorochlorocarbon parting liquids other thantrichlorofluoromethane can be used, the test described in Example I wasrepeated, using CClF₂ CClF₂ (dichlorotetrafluoroethane) as the partingliquid.

In this test the ash content of the product coal was 13.0 percent whichis virtually indistinguishable from the result obtained in the testdescribed in Example I. The weight yield was a slightly lower 56.6percent.

The test shows that trichlorofluoromethane is not the only one of thelisted fluorochlorocarbons which can be used in the gravity separationof coal from foreign material.

EXAMPLE III

A test as described in Example I was made to demonstrate the advantagesof adding a surface active agent to the parting liquid. The results arecompared to those obtained by Warner Laboratories, Inc., Cresson, Pa. inthe standard washability study of the coal in Table 4 below.

The coal was that from the Upper Freeport seam (see Examples I and II).The parting liquid was trichlorofluoromethane, and about two pounds ofsurface active agent per ton of coal was employed. The particularsurface active agent selected for the test was Pace Perk. As discussedabove this is an ionic surface active agent which consists primarily ofsalts of dodecylbenzenesulfonic acid. The surface active agent was mixedwith the parting liquid before the coal was added.

                  Table 4                                                         ______________________________________                                                   Run-of-mine                                                                            Washability                                                                              Present                                                   Coal     Study      Invention                                      ______________________________________                                        Volatile Matter %                                                                          28.42                 34.77                                      Fixed Carbon %                                                                             46.03                 59.55                                      Ash %        25.55      8.9        5.68                                        lbs/m BTU   23.5                  3.98                                        % Red'n/m BTU                     83                                         Total Suflur %                                                                             1.46       0.95       0.52                                        lbs/m BTU   1.34                  0.36                                        % Red'n/m BTU                     72.8                                       Pyritic Sulfur %                                                                           1.09                  0.16                                        lbs/m BTU   1.00                  0.11                                        % Red'n/m BTU                     88.8                                       Organic Sulfur %                                                                           0.35                  0.32                                        lbs/m BTU   0.32                  0.22                                        % Red'n/m BTU                     30                                         BTU/lb       10,891                14,262                                     BTU/lb (MAF) 14,629                15,121                                     Weight Yield %          64.9       68.5                                       BTU Yield %                        89.7                                       Specific Gravity*       1.55       1.51                                       Moisture (input)                                                                           7.1                   7.1                                        Coke Button**                                                                              7                     8.5                                        Recovered Coal                     2.18                                        Moisture                                                                     ______________________________________                                         m BTU = 10.sup.6 BTU                                                          REd'n = reduction                                                             MAF = moisture and ash free basis?                                            *of the parting liquid                                                        **The coke button value (or more formally, free swelling index) is a          measure of cokability. FSI values range from 0-10 with the higher value       being ideal. Coals with a FSI of less than 5 are essentially useless as       coking coals.                                                                 The above notes also apply to the tables which follow.                   

A number of significant points are shown by the data tabulated above.

The ash content of the coal was not only reduced, it was reduced 36percent below the level which it theoretically could be as determined bythe standard washability study.

Total sulfur was reduced by 72.8 percent; this was 45 percent betterthan obtained in the standard washability study. Pyritic sulfur wasalmost completely separated from the coal, and there was a significantreduction in organic sulfur. As mentioned above, this is a result whichno other coal cleaning process known to us is capable of achieving.

Furthermore, the cokability of the coal was significantly improved.

EXAMPLE IV

To demonstrate that other surface active agents can be employed and invarying amounts, bench scale coal cleaning tests were made using UpperFreeport coal with the size consist and other characteristics describedin Example I.

The parting liquid was trichlorofluoromethane.

The surface active agents employed in the tests and the amounts usedwere:

                  Table 5                                                         ______________________________________                                        Test       Surface Active Agent                                               ______________________________________                                        A          Aerosol OT-100 (American Cyanamid)                                 anionic surfactant, dioctyl                                                              ester of sodium sulfosuccinic                                                 acid; 0.06 pounds per ton of coal                                  B          Same as in Test A; 0.6 pounds per                                             ton of coal                                                        C          Witcomine 235 (Witco Chemical                                                 Corp.) - cationic surfactant,                                                 1-polyaminoethyl-2n-alkyl-2-                                                  imidazoline; three pounds per                                                 ton of coal                                                        D          Same as Test C; 0.03 pounds per                                               ton of coal                                                        E          Same as Tests A and B; 0.33                                                   pounds per ton of coal plus                                                   No. 6 fuel oil, 0.67 pounds                                                   per ton of coal                                                    ______________________________________                                    

The results of tests A-E are tabulated in Table 6 below.

                  Table 7                                                         ______________________________________                                                   Run-of-mine                                                                   Coal       Test F    Test G                                        ______________________________________                                        Ash %        24.82        9.52      12.61                                      % Red'n/m BTU            68.0      58.5                                      Total Sulfur %                                                                             6.73         2.88      3.76                                       % Red'n/m BTU            62.8      54.2                                      Pyritic Sulfur %                                                                           4.34         1.07      1.02                                       % Red'n/m BTU            76.4      80.6                                      Organic Sulfur %                                                                           2.31         1.80      2.68                                       % Red'n/m BTU            43.4      5.1                                       BTU/lb       10,359       12,877    12,649                                    Weight Yield %            62.8      60.5                                      BTU Yield %               77.6      76.5                                      Moisture %   6.5          6.0       6.0                                       ______________________________________                                    

The data in Table 6 shows that the particular surface active agent usedis not critical, that both anionic and cationic materials aresatisfactory, and that the agent need not be one which wouldconventionally be considered a surfactant.

The tabulated data also shows that the amount of surface active agentcan be varied by as much as two orders of magnitude (depending upon theparticular agent employed). The larger amounts in general increase theefficiency of the cleaning process though not in direct proportion tothe amount used.

EXAMPLE V

In another pair of tests showing that the surface active agents weemploy need not be conventional surfactants, Ohio No. 9 coal with a 60mesh×0 size consist was cleaned using the bench scale proceduredescribed above.

The parting liquids were:

Test F--CCl₃ F plus Cal-Supreme, 0.1 percent by volume, and

Test G--CCl₃ F plus 5 percent by volume No. 4 fuel oil.

The results of the tests are shown in Table 7.

                  Table 7                                                         ______________________________________                                                   Run-of-mine                                                                   Coal       Test F    Test G                                        ______________________________________                                        Ash %        24.82        9.52      12.61                                      % Red'n/m BTU            68.0      58.5                                      Total Sulfur %                                                                             6.73         2.88      3.76                                       % Red'n/m BTU            62.8      54.2                                      Pyritic Sulfur %                                                                           4.34         1.07      1.02                                       % Red'n/m BTU            76.4      80.6                                      Organic Sulfur %                                                                           2.31         1.80      2.68                                       % Red'n/m BTU            43.4      5.1                                       BTU/lb       10,359       12,877    12,649                                    Weight Yield %            62.8      60.5                                      BTU Yield %               77.6      76.5                                      Moisture %   6.5          6.0       6.0                                       ______________________________________                                    

Both the No. 4 fuel oil and the cationic surfactant were effective withthe latter proving to be somewhat more so in this particular test.

EXAMPLE VI

It was pointed out above that more efficient cleaning can in some, ifnot all, cases be obtained if the slurry of coal 1,2-difluoroethane or,fluorochlorocarbon, and surface active agent is agitated before thegravity separation of the coal is effected.

This is shown by a test which duplicated test B, Example IV except thatthe slurry of coal and parting liquid (which contained 60 percent byweight solids) was mechanically agitated using a blender for two minutesbefore gravity separation was effected. The blending action did notreduce the size consist significantly.

The results of this test, identified as "H", are compared to thoseobtained in Test B in Table 8 below.

                  Table 8                                                         ______________________________________                                                    Run-of-mine                                                                   Coal      Test B   Test H                                         ______________________________________                                        Volatile Matter %                                                                           26.09                36.01                                      Fixed Carbon %                                                                              37.34                57.73                                      Ash %         35.57       6.55     6.26                                        lbs/m BTU    40.1                 4.4                                         % Red'n/m BTU                     88.9                                       Total sulfur %                                                                              1.55                 0.87                                        lbs/m BTU    1.70                 0.62                                        % Red'n/m BTU                     63.7                                       Pyritic Sulfur %                                                                            1.22                 0.31                                        lbs/m BTU    1.33                 0.22                                        % Red'n/m BTU                     83.5                                       Organic Sulfur %                                                                            0.31                 0.50                                        lbs/m BTU    0.34                 0.35                                        % Red'n/m BTU                                                                BTU/lb         9,128               14,113                                     BTU/lb (MAF)  14,391               15,056                                     Weight Yield %            52.3     52.3                                       BTU Yield %                        80.9                                       Specific Gravity          1.51     1.51                                       ______________________________________                                    

As shown by the tabulated data, agitation of the coal and parting liquidslurry resulted in a further, significant reduction in the ash contentof the coal without reducing the weight yield or otherwise adverselyeffecting the cleaning process.

EXAMPLE VII

As indicated above, our novel process has the capability of cleaningcoal of different size consists.

This was demonstrated by repeating the test described in Example IIIafter having first ground the coal to a size consist of 60 mesh×0. Theresults of the two tests are compared in Table 9.

                  Table 9                                                         ______________________________________                                                   Run-of-mine                                                                            Example III                                                                              60 Mesh                                                   Coal     Test       × 0 Coal                                 ______________________________________                                        Volatile Matter %                                                                          28.42      34.77      36.61                                      Fixed Carbon %                                                                             46.03      59.55      57.84                                      Ash %        25.55      5.68       5.55                                        lbs/m BTU   23.5       3.98       3.89                                        % Red'n/m BTU          83         83.4                                       Total Sulfur %                                                                             1.46       0.52       0.73                                        lbs/m BTU   1.34       0.36       0.51                                        % Red'n/m BTU          72.8       61.8                                       Pyritic Sulfur %                                                                           1.09       0.16       0.10                                        lbs/m BTU   1.00       0.11       0.07                                        % Red'n/m BTU          88.8       93                                         Organic Sulfur %                                                                           0.35       0.32       0.59                                        lbs/m BTU   0.32       0.22       0.41                                        % Red'n/m BTU          30                                                    BTU/lb       10,891     14,262     14,253                                     BTU/lb (MAF) 14,629     15,121     15,091                                     Weight Yield %          68.5       68.8                                       BTU Yield %             89.7       90.0                                       Specific Gravity        1.51       1.51                                       Moisture (input)                                                                           7.1        7.1        7.1                                        Coke Button  7          8.5        8                                          Recovered Coal          2.18       2.22                                       Moisture                                                                      ______________________________________                                    

The results were nearly the same and probably within the limits ofexperimental error. The significant point in this test is that there wasessentially no loss in BTU yield even though in one case (Example III)the particle size was 3/8 inch×0 and in the other 60 m×0.

EXAMPLE VIII

We also pointed out above that the specific gravity of the1,2-difluoroethane and fluorochlorocarbons we employ as parting liquidscan be readily adjusted in applications where this is advantageous. Asan example, the specific gravity may be lowered to separate more ashfrom the coal in applications where the customer's specifications sodictate.

That the specific gravity of our parting liquids can be readily adjustedwas demonstrated by a series of bench scale tests in which petroleumether was mixed with trichlorofluoromethane in amounts which reduced thespecific gravity of the mixtures to 1.47 and 1.43. These mixtures andtrichlorofluoromethane alone, all with three pounds of Pace Perk per tonof coal, were used as parting liquids.

Upper Freeport coal with the size consist described in Example I wascleaned.

The results are tabulated in Table 10.

                                      Table 10                                    __________________________________________________________________________                     Test Product,                                                                        Test Product,                                                                         Test Product,                                           Run-of-mine                                                                          CCl.sub.3 F                                                                          CCl.sub.3 F mixture,                                                                  CCl.sub.3 F mixture                                     Coal   s.g. 1.51                                                                            s.g. 1.47                                                                             s.g. 1.43                                     __________________________________________________________________________    Volatile Matter %                                                                       26.09  36.75  37.36   36.31                                         Fixed Carbon %                                                                          37.34  55.36  56.34   58.11                                         Ash %     35.57  7.89   6.30    5.58                                           lbs/m BTU                                                                              40.1   5.67   4.46    3.9                                            % Red'n/m BTU   85.9   88.9    90.3                                          Total Sulfur %                                                                          1.55   0.98   0.93    0.92                                           lbs/m BTU                                                                              1.70   0.70   0.67    0.64                                           % Red'n/m BTU   58.6   60.7    62.2                                          Pyritic Sulfur %                                                                        1.22   0.53   0.37    0.40                                           lbs/m BTU                                                                              1.33   0.38   0.27    0.28                                           % Red'n/m BTU   71.4   80.0    79.0                                          Organic Sulfur %                                                                        0.31   0.43   0.54    0.50                                           lbs/m BTU                                                                              0.34   0.31   0.39    0.35                                           % Red'n/m BTU   9                                                            BTU/lb     9,128 13,911 14,138  14,311                                        BTU/lb (MAF)                                                                            14,391 15,103 15,089  15,158                                        Weight Yield %   52.8   54.1    51.7                                          BTU Yield %      80.5   83.8    81.1                                          Specific Gravity 1.51   1.47    1.43                                          __________________________________________________________________________

The data shows that the percentage of ash reduction increased as thespecific gravity of the parting liquid was lowered. There was acorresponding beneficial increase in the percentage of sulfur reduction,and the removal of more ash and sulfur was accomplished without asacrifice in BTU yield.

EXAMPLE IX

Numerous bench scale tests conducted in the manner described above showthat our novel process is useful for cleaning coals in general asopposed to coal from a particular seam. Results of various testsinvolving coal from the Upper Freeport seam are described in thepreceding examples, and results of exemplary tests involving other coalsare tabulated in Table 11.

Trichlorofluoromethane plus 0.5 volume percent of Pace Perk was used asa parting liquid in cleaning the Midwestern (Illinois No. 5 and Ohio No.9) coals, and CCl₃ F was used alone as a parting liquid to clean theAppalachian (Lower Kittanning) coal.

                                      Table 11                                    __________________________________________________________________________              Lower Kittanning                                                                          Illinois No. 5                                                                            Ohio No. 9                                            (5 mesh × 0)                                                                        (3/8 in. × 0)                                                                       (60 mesh × 0)                                   Run-of-mine                                                                          Test Run-of-mine                                                                          Test Run-of-mine                                                                          Test                                           Coal   Product                                                                            Coal   Product                                                                            Coal   Product                              __________________________________________________________________________    Ash %     26.38  9.63 9.22   4.79 24.82  9.52                                  % Red'n/m BTU   70.8        60.6        68.0                                 Total Sulfur %                                                                          1.46   .73  1.89   1.32 6.73   2.88                                  % Red'n/m BTU   60.2        35.5        62.8                                 Pyritic Sulfur %                                                                        1.05   .25  1.22   .74  4.34   1.07                                  % Red'n/m BTU   81.0        41.9        76.4                                 Organic Sulfur %                                                                        .39    .46  .65    .54  2.31   1.80                                  % Red'n/m BTU   6.0         22.0        43.4                                 BTU/lb    10,844 13,595                                                                             13,116 13,800                                                                             10,359 12,877                               Weight Yield %   67.9        93.3        62.8                                 BTU Yield %      85.0        98.2        77.6                                 Moisture %                                                                              5.0    5.0  10.45  8.90 6.5    6.0                                  __________________________________________________________________________

The data shows that our process can be employed to clean coals of widelydivergent character. The run-of-mine ash contents of the coals, forexample, vary by a ratio of 2.9:1. Also, the tabulated data againdemonstrates that a fluorochlorocarbon alone can be used as a partingliquid in our process.

EXAMPLE X

A bench scale test conducted as described above and usingtrichlorofluoromethane plus Aerosol OT-100 (0.3 lbs/ton coal) as theparting liquid demonstrates that our novel process is so efficient thatit can even be used to separate substantial amounts of ash and sulfurfrom the product coal of a modern hydrobeneficiation plant.

The coal employed was Pittsburgh No. 8 Washing Plant Product. It wasground to 5 mesh×0 before it was cleaned.

The results of the test are shown in Table 12.

                  Table 12                                                        ______________________________________                                                    Washing Plant                                                                 Product Coal                                                                              Test Product                                          ______________________________________                                        Ash %         15.96         7.52                                               % Red'n/m BTU              57.6                                              Total Sulfur %                                                                              4.30          3.85                                               % Red'n/m BTU              10.4                                              Pyritic Sulfur %                                                                            2.70          1.74                                               % Red'n/m BTU              35.5                                              Organic Sulfur %                                                                            1.59          2.10                                               % Red'n/m BTU                                                                BTU/lb        12,375        13,740                                            Weight Yield %              82.6                                              BTU Yield %                 91.7                                              Moisture %    6.0           6.0                                               ______________________________________                                    

In this test, the ash and sulfur contents of coal already cleaned in amodern facility were reduced by values of 57 and 10 percent with no lossof BTU Yield by cleaning the coal with our novel process.

EXAMPLE XI

Two representative bench scale tests as described above illustrate thecapability of pure trichlorofluoromethane to effect a removal of organicsulfur from Ohio No. 9 coal and an enhancement of this property when 0.5weight percent of Cal-Supreme surfactant is added to the parting liquid.

The size consist in both tests was 60 m×0, and the moisture content ofthe raw coal was 6 percent.

The results of the tests are tabulated below.

                  Table 13                                                        ______________________________________                                                                     Case II                                                            Case I     Cal-Supreme                                                Raw Coal                                                                              No Additive                                                                              Additive                                         ______________________________________                                        Ash %       24.82     22.55      9.46                                          % Red'n/m BTU        13.6       68.4                                         Total Sulfur %                                                                            6.73      5.39       2.69                                          % Red'n/m BTU        23.6       65.4                                         Pyritic Sulfur %                                                                          4.34      3.06       0.97                                          % Red'n/m BTU        32.8       78.7                                         Organic Sulfur %                                                                          2.31      2.27       1.69                                          % Red'n/m BTU        6.3        47.2                                         BTU/lb      10,359    10,867     12,957                                       Weight Yield %        56.6       59.5                                         BTU Yield %           59.4       73.9                                         ______________________________________                                    

The foregoing are exemplary of a multitude of tests in which, by using afluorochlorocarbon, alone and with various surface active agents, wehave removed sulfur from a fresh coal sample to an extent which exceeds100 percent of the sum of the pyritic (and sulfate) sulfur concentrationin the original coal without undue loss of BTU Yield. This isaccomplished without change of the normal sink-float separationprocedure.

Furthermore, organic sulfides and sulfones have been observed in theparting liquid residue by infrared techniques whereas, as indicatedabove, no other sink-float process of which we are aware causes organicsulfur reduction.

EXAMPLE XII

In an even more demanding test than that described in Example X, slurrypond coal was cleaned by our process. Heretofore, there has not been anyway to recover coal from slurry ponds because of the small size of theparticles and the high moisture content.

The size consist of the coal in the slurry pond was 85 percent less than200 mesh and 67 percent less than 325 mesh.

Trichlorofluoromethane with approximately one pound of Aerosol OT-100per ton of coal was used as the parting liquid.

In Table 14 below we have compared the raw slurry pond coal and theproduct coals obtained by cleaning that coal at input bed moistures ofeight and 14 percent.

                  Table 14                                                        ______________________________________                                                           Test Product                                                                             Test Product                                               Raw Slurry                                                                            Coal - 8%  Coal - 14%                                                 Pond    Moisture   Moisture                                                   Coal    Input      Input                                           ______________________________________                                        Volatile Matter %                                                                          22.60     28.01      27.43                                       Fixed Carbon %                                                                             47.75     66.71      66.24                                       Ash %        29.65     5.28       6.33                                        lbs/m BTU    29.1      3.64       4.43                                        % Red'n/m BTU          87.5       84.8                                        Total Sulfur %                                                                              0.85     0.81       0.80                                        lbs/m BTU     0.83     0.56       0.56                                        % Red'n/m BTU          32.5       32.5                                        Pyritic Sulfur %                                                                            0.41     0.19       0.16                                        lbs/m BTU     0.40     0.13       0.11                                        % Red'n/m BTU          67.5       72.5                                        Organic Sulfur %                                                                            0.39     0.56       0.58                                        lbs/m BTU     0.38     0.39       0.41                                        % Red'n/m BTU                                                                 BTU/lb       10,189    14,520     14,297                                      BTU/lb (MAF) 14,483    15,329     15,263                                      Weight Yield %         37.1       37.3                                        BTU Yield %            53         52.3                                        Specific Gravity %     1.50       1.50                                        Raw Coal %             8          14                                          (Input Moisture)                                                              Product Coal %         4.24       4.3                                         (Moisture)                                                                    Coke Button  1         9          9                                           ______________________________________                                    

The recovered coal is highly marketable.

The cost of recovering and cleaning slurry pond coal as employed in thejust described test is, conservatively calculated, $3.00 per input ton.On the other hand, the current F.O.B. market price for the product is atleast $25.00 to $35.00 per ton, which shows that this application of ourprocess is one of considerable economic importance.

This test is also significant because of the large amount of water thatreported to the sinks in the cleaning process. As shown in Table 14,this resulted in a reduction of water content from 14 to 4.3 percent.That is, without any additional steps, over two-thirds of the initiallypresent water was removed from the coal.

That this large proportion of the water can be caused to report to thesinks is attributable to the novel 1,2-difluoroethane orfluorochlorocarbon and additive systems we employ as parting liquids.Because the parting liquids are essentially chemically inert under theprocess conditions, we can mix them a surface active agent which willdisrupt the water films on the surfaces of the coal particles and removethe water to the sinks.

This is opposite to what has heretofore been done in coal cleaningprocesses such as described in the Foulke et al patents identifiedabove. Those processes employ parting liquids which, because of theirchemical reactivity and/or high boiling points, can not be recovered inamounts which make the process practical if they are allowed to directlycontact the coal. Therefore, these processes use surfactants of acharacter which, instead of disrupting the water films on the coalparticles, stabilize these films so they will isolate the coal particlesfrom the parting liquid. No water is removed from the coal by theseprocesses, and additional processing may be necessary to reduce themoisture content of the product to an acceptable level.

EXAMPLE XIII

The following tests are representative of many which show that theresults described and discussed in the preceding examples are equallyattainable when coal is cleaned by our process on a much larger scale.

The tests were conducted in the pilot plant illustrated in FIG. 11 usingthe pilot plant test procedure described above.

The coal was that described in Example I. Trichlorofluoromethane withone pound of Aerosol OT-100 per ton of coal was used as the partingliquid.

The test results are reported in Table 15. They are compared with theresults obtained in the 1.51 specific gravity parting liquid testdescribed in Example VIII. The latter was a bench scale test, butotherwise the same.

Throughputs in the range of six tons per hour were employed. Six hundredand ten pounds of coal were cleaned in the first test and 582 pounds inthe second test.

                  Table 15                                                        ______________________________________                                                            610     582     Example                                              Run-of-mine                                                                            pound   pound   VIII                                                 coal     Test    Test    Test                                      ______________________________________                                        Volatile Matter %                                                                          26.09      36.63   26.62 36.75                                   Fixed Carbon %                                                                             37.34      55.72   56.08 55.36                                   Ash %        35.57      7.65    7.30  7.89                                    lbs/m BTU    40.1       5.5     5.2   5.67                                    % Red'n/m BTU           86.3    87    85.9                                    Total Sulfur %                                                                             1.55       0.88    0.88  0.98                                    lbs/m BTU    1.70       0.63    0.63  0.70                                    % Red'n/m BTU           62.8    63    58.6                                    Pyritic Sulfur %                                                                           1.22       0.67    0.56  0.53                                    lbs/m BTU    1.33       0.48    0.40  0.38                                    % Red'n/m BTU           64      70.2  71.4                                    Organic Sulfur %                                                                           0.31       0.19    0.28  0.43                                    lbs/m BTU    0.34       0.14    0.2   0.31                                    % Red'n/m BTU           62      44.5  9                                       BTU/lb       9,128      13,096  14,009                                                                              13,911                                  BTU/lb (MAF) 14,391     15,058  15,112                                                                              15,103                                  Weight Yield %          54.4    54.8  52.8                                    BTU Yield %             83.0    84.1  80.5                                    Specific Gravity        1.51    1.51  1.51                                    ______________________________________                                    

The data shows that the results of the two pilot plant runs wereconsistent and, if anything, superior to those obtained in the benchscale tests although the differences may be within the level ofexperimental error.

Tests on other coals produced similar results. Those obtained incleaning Lower Kittanning coal and the hydrobeneficiation plant product(Example X) are typical.

The coal and parting liquids were as described in Example X except thatthe hydrobeneficiation product had a size consist of 5 mesh×0 and theLower Kittanning coal had a size consist of 3/8 inch×0 rather than 30mesh×0 as in the bench scale test.

Results of the tests appear in Table 16.

                  Table 16                                                        ______________________________________                                                               Hydrobeneficiation                                                Lower Kittanning                                                                          Product Coal                                                      Bench  Pilot    Bench    Pilot                                                Scale  Plant    Scale    Plant                                     ______________________________________                                        Ash %        9.63     10.73    7.52   6.08                                    % Red'n/m BTU                                                                              70.8     67.4     57.6   64.0                                    Total Sulfur %                                                                             .73      .77      3.85   3.53                                    % Red'n/m BTU                                                                              60.2     57.9     10.4   29.4                                    Pyritic Sulfur %                                                                           .25      .25      1.74   1.49                                    % Red'n/m BTU                                                                              81.0     81.0     35.5   51.0                                    Organic Sulfur %                                                                           .46      .50      2.10   2.02                                    % Red'n/m BTU                                                                              6.0                                                              BTU/lb       13,595   13,535   13,740 13,964                                  Weight Yield 67.9     70.5     82.6   80                                      BTU Yield    85.0     88.0     91.7   89.5                                    Moisture %   5.0      5.0      6.0    6.0                                     ______________________________________                                    

Table 16 shows that the results of the pilot plant and bench scale testsinvolving the cleaning of Lower Kittanning and hydrobeneficiated coalswere very much alike. Again, the pilot plant was slightly superior tothe bench apparatus.

EXAMPLE XIV

It was pointed out above that our invention includes a novel process foruniformly dispersing additives on coal and that one application of thisprocess is the dustproofing of coal.

A goal in dustproofing coal is to agglomerate the smaller particles intolarger ones, thereby making the product easier to handle, less subjectto attrition in storage, etc.

To illustrate how coal can be dedusted in accord with the principles ofthe present invention, No. 6 fuel oil was dissolved intrichlorofluoromethane with stirring at room temperature in a ratio ofone part of fuel oil to 250 parts of fluorochlorocarbon.

The liquid was mixed with coal which was ground to a 30 mesh×0 sizeconsist in amounts providing approximately two pounds of fuel oil perton of coal.

The coal was first drip dried, and the remaining fluorochlorocarbon wasthen removed by evaporation.

The size consists of the treated and untreated coals are compared inTable 17.

In the table which follows, the numerical entries are the weight percentof the sample which passed through a sieve of the mesh size indicated onthe same horizontal line as the numerical entry.

                  Table 17                                                        ______________________________________                                        Sieve Mesh Size                                                                              Untreated    Treated                                           ______________________________________                                         30 × 0  98.5         96.6                                               60 × 0  71.7         58.0                                              100 × 0  53.4         25.9                                              200 × 0  36.1          4.7                                              ______________________________________                                    

The tabulated data shows that the treatment effectively reduced theproportion of small particles. Furthermore, the dedusted particles thatdid pass the finer mesh sieves had a marked tendency to agglomerate andto support an angle of repose exceeding 90°.

EXAMPLE XV

As discussed above, another application of our novel coating andadditive dispersing process is the waterproofing of coal to keep it fromspontaneously igniting following the absorption of water and/or to keepthe lumps or particles from freezing together under low temperatureconditions.

The effectiveness of our process in waterproofing coal is demonstratedby a test in which a kilogram of a Wyoming coal with a size consist of3/4 inch×0 and an inherent moisture content of thirty percent wascompletely dried in a vacuum oven at 105° C. The coal was divided intotwo samples, and one was immediately transferred to a gastightcontainer.

The second sample was with equal alacrity immersed in a mixture of 97percent by volume trichlorofluoromethane and 3 percent by volume No. 6fuel oil. The mixture was stirred for 0.5 minute to promote intimatecontact between the coal and the mixture of carrier and waterproofingagent.

The coal was then extracted from the bath and the trichlorofluoromethaneremoved by evaporation.

Both the treated and untreated samples were immersed in deionized waterunder ambient conditions. One hour later the water was removed byshaking the samples of coal on a screen.

The water recovered from the coal was compared to the amount present atthe beginning of the test, the difference being water absorbed on andadsorbed by the coal.

The untreated coal acquired a 50 percent moisture content almostinstantaneously and equiliberated through air drying to a 30 percentmoisture content. In contrast, the shake dried, treated sample had amoisture content of only twenty percent after the one hour submersion.

When air dried to the same extent as the first sample, i.e., to 30percent moisture, the treated sample had only 1.5 percent absorbedmoisture as determined by vacuum oven drying at 105° C. This indicatedthat the porous structure of the coal had, indeed, been inhibited fromcarrying moisture. The level was well below the limit of 5 percentneeded to insure against spontaneous combustion and freezing of the coalinto a mass.

EXAMPLE XVI

Another previously discussed aspect of our invention is the conversionof coal particles into briquettes and similar artifacts which facilitatetransportation, reduce storage losses, and permit proper gas flowthrough the system in application such as coking.

Exemplary briquettes were made by immersing 60×0 mesh Pittsburgh coal ina mixture of 97 percent volume trichlorofluoromethane and 3 percent No.6 fuel oil and manually stirring the mixture for less than a minute.

The coal was recovered and the trichlorofluoromethane removed byevaporation, leaving the coal coated with the fuel oil in an amount ofapproximately one gallon of fuel oil per ton of coal.

The coated coal was transferred to a die and compacted into one-inchdiameter by two-inch long cylinders under 3000 pounds pressure by ahydraulic machine.

Without further treatment the briquettes were dropped onto a concretefloor from a height of four feet.

This did not cause any substantial damage to the briquettes.

Numerous embodiments of our invention have been described above invarying degrees of detail. However, the invention may be embodied instill other specific forms without departing from the spirit oressential characteristics thereof. The present embodiments are thereforeto be considered in all respects as illustrative and not restrictive,the scope of the invention being indicated by the appended claims ratherthan by the foregoing description; and all changes which come within themeaning and range of equivalency of the claims are therefore to beembraced therein.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. In that method of beneficiating coal to separate itfrom foreign material mixed therewith in which the coal is introducedinto a body of parting liquid which is or contains a halogenatedhydrocarbon and has a specific gravity intermediate those of the coaland foreign material so that the coal will rise toward the top of thebody of liquid and the foreign material will sink toward the bottomthereof, the improvement wherein any halogenated hydrocarbon present inthe parting liquid is 1,2-difluoroethane or a fluorochloro derivative ofmethane or ethane selected from the group consisting of1-chloro-2,2,2-trifluoroethane, 1-1-dichloro-2,2,2-trifluoroethane,dichlorofluoromethane, 1-chloro-2-fluoroethane,1,1,2-trichloro-1,2,2-trifluoroethane,1,1-dichloro-1,2,2,2-tetrafluoroethane, and trichlorofluoromethane.
 2. Amethod of beneficiating coal according to claim 1 in which the coal tobe cleaned is preconditioned with a mixture of 1,2-difluoroethane or afluorochloro derivative as aforesaid and a surface active agent beforesaid coal is introduced into the body of parting liquid.
 3. A method ofbeneficiating coal according to claim 2 in which 0.03 to six pounds ofsurface active agent per ton of coal is employed to precondition thecoal.
 4. A method of beneficiating coal according to claim 2 in whichthe surface active agent is an ionic surfactant.
 5. A method ofbeneficiating coal according to claim 2 in which the surface activeagent is an ester or salt of a sulfosuccinic acid.
 6. A method ofbeneficiating coal according to claim 2 in which the surface activeagent is a lower alkyl or alkylene amine.
 7. A method of beneficiatingcoal according to claim 2 in which the surface active agent is No. 4 orNo. 6 fuel oil.
 8. A method of beneficiating coal according to claim 2together with the step of agitating the coal and the mixture of1,2-difluoroethane or fluorochloro derivative and surface active agent.9. A method of beneficiating coal according to claim 2 in which thespecific gravity of the body of parting liquid is controlled by mixing adiluent which is a petroleum fraction or a liquid alkane with the1,2-difluoroethane or fluorochloro derivative and coal in thepre-conditioning step in an amount sufficient to reduce the specificgravity of the parting liquid to not less than about 1.30.
 10. A methodof beneficiating coal according to claim 9 in which the diluent is apetroleum ether.
 11. A method of beneficiating coal according to claim 9in which the diluent is pentane.
 12. A method of beneficiating coalaccording to claim 1 in which the only halogenated hydrocarbon presentin the parting liquid is trichlorofluoromethane.
 13. A method ofbeneficiating coal according to claim 1 which includes the step ofrecovering parting liquid from the separated coal and the foreignmaterial from which the coal is separated.
 14. A method of beneficiatingcoal according to claim 1 in which the parting liquid is removed fromthe coal and/or rejects by evaporation.
 15. A method of beneficiatingcoal according to claim 14 wherein parting liquid is recovered from theforeign material and the coal by drip drying.
 16. A method ofbeneficiating coal according to claim 15 in which the coal and foreignmaterial are thereafter subjected to a vacuum to evolve additionalparting liquid therefrom and in which the parting liquid is thenrecovered by compressing and condensing the evolved vapor.
 17. A methodof beneficiating coal according to claim 15 in which the coal andforeign material are thereafter purged with air to strip additionalparting liquid therefrom in vapor form and wherein the parting liquid isthen recovered by compressing and condensing the air/vapor mixture toseparate the parting liquid from noncondensible gases present in themixture.
 18. A method of beneficiating coal according to claim 15together with the step of purging the coal and foreign material to stripadditional parting liquid therefrom and wherein the parting liquid isthen recovered by selectively absorbing the parting liquid in a liquidabsorbent, heating the absorbent to release the parting liquidtherefrom, and recovering the parting liquid.
 19. A method ofbeneficiating coal according to claim 18 together with the steps ofcooling the absorbent after the parting liquid has been releasedtherefrom to increase its absorbent capacity, recovering heat rejectedin the step of cooling the absorbent, and adding said heat to liquidabsorbent in which parting liquid is entrained.
 20. A method ofbeneficiating coal according to claim 1 in which the coal is abituminous coal.
 21. A method of beneficiating coal according to claim 1in which the coal is the product of a hydrobeneficiation process.
 22. Amethod of beneficiating coal according to claim 1 in which the coal isfrom the residue of a coal cleaning process.
 23. A method ofbeneficiating coal according to claim 1 in which the coal and associatedforeign material is reduced to particles which are predominantly lessthan 200 mesh in diameter prior to introducing the coal and foreignmaterial into the body of parting liquid so that essentially all pyritepresent will separate from the coal in the body of parting liquid.
 24. Amethod of beneficiating coal according to claim 1 together with the stepof adding to the coal before it is cleaned an additive capable ofaltering the physical and/or chemical characteristics of the clean coalor the foreign material from which the coal is separated or both theclean coal and the foreign material.
 25. A method of beneficiating coalaccording to claim 1 together with the step of dispersing in the body ofparting liquid an additive capable of altering the physical and/orchemical characteristics of the clean coal or the foreign material fromwhich the coal is separated or both the clean coal and the foreignmaterial.
 26. A method of beneficiating coal according to claim 1 whichincludes the step of recovering middlings from said body of partingliquid independently of said coal and said foreign material.
 27. Amethod of beneficiating coal according to claim 1 in which said body ofparting liquid is in a gravity separator and the separation of the coalfrom the foreign material is thereby carried out in a separator asaforesaid.
 28. A method of beneficiating coal according to claim 1 inwhich said body of parting liquid is in a centrifugal separator and theseparation of the coal from the foreign material is thereby carried outin a separator as aforesaid.
 29. A method of reducing the organic sulfurcontent of coal comprising the step of bringing into intimate contactwith the coal an effective amount of a liquid which is1,2-difluoroethane or a fluorochloro derivative of methane or ethaneselected from the group consisting of 1-chloro-2,2,2-trifluoroethane,1-1-dichloro-2,2,2-trifluoroethane, dichlorofluoromethane, 1-chloro-2-fluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane,1,1-dichloro-1,2,2,2-tetrafluoroethane, and trichlorofluoromethane. 30.Coal cleaning apparatus, comprising: a separator in which coal andforeign matter can be separated by a parting liquid; means for supplyingcoal to be cleaned to said separator in admixture with parting liquid asaforesaid; and means for adjusting the specific gravity of said partingliquid, said last-mentioned means comprising means for reducing thepressure on said parting liquid to a level at which a portion of saidparting liquid will convert to vapor, thereby extracting heat from,reducing the temperature of, and increasing the specific gravity of saidliquid.
 31. Coal cleaning apparatus according to claim 30 in which themeans for adjusting the specific gravity of the parting liquid includesa conditioner for the coal and parting liquid admixture ahead of and incommunication with said separator and means for communicating theinterior of said conditioner with a reduced pressure source.
 32. Coalcleaning apparatus according to claim 31 together with means responsiveto the temperature of the liquid in the conditioner for automaticallycontrolling the pressure on the liquid in the conditioner and therebyautomatically regulating the specific gravity of the parting liquid. 33.Coal cleaning apparatus comprising: a separator in which coal andforeign material can be separated by a parting liquid and heat exchangemeans for varying the apparent temperature of the coal to be cleanedbefore it is introduced into the separator to thereby control thespecific gravity of the parting liquid in the separator.
 34. Coalcleaning apparatus according to claim 33 wherein the means for varyingthe apparent temperature of the coal includes a conditioner in which aslurry of the coal and parting liquid can be formed and means fortransferring the slurry from the conditioner to the separator, said heatexchange means comprising a heat exchanger in said conditioner and meansfor circulating a heat transfer fluid into heat transfer relationshipwith said heat exchanger.
 35. Coal cleaning apparatus, comprising: aseparator; a parting liquid in said separator for separating coal andforeign material introduced thereinto; and means for conditioning thecoal to be cleaned before it is introduced into said separator whichincludes means for mixing parting liquid as aforesaid and a surfaceactive agent with said coal.
 36. Coal cleaning apparatus according toclaim 35 in which said conditioning means includes means for agitatingsaid coal to blend parting liquid and surface active agent therewith.37. Coal cleaning apparatus, comprising: a separator in which coal andforeign material can be separated by a parting liquid; means in whichparting liquid can drain from coal and foreign material discharged fromsaid separator; means for heating said coal and said foreign material tovaporize and thereby separate additional parting liquid therefrom in thegaseous state; and means for recovering the vaporized parting liquid andconverting it to liquid form, the means for recovering the partingliquid including means in which said gas can be absorbed in a liquidabsorbent and means for thereafter heating said absorbent to release theparting liquid therefrom.
 38. Coal cleaning apparatus according to claim37 together with means for cooling the liquid absorbent from which theparting liquid has been separated and means for recovering the heatrejected from the liquid absorbent in the cooling means and adding therecovered heat to the liquid absorbent on the upstream side of theheating means to thereby reduce the load on said heating means.
 39. Coalcleaning apparatus comprising: a separator in which coal and foreignmaterial can be separated by a parting liquid; means in which partingliquid can drain from coal and foreign material discharged from saidseparator; means for heating said coal and foreign material to vaporizeand thereby separate additional parting liquid therefrom in the gaseousstate; means for recovering vaporized parting liquid from said heatingmeans and/or other components of said apparatus; means for circulatingrecovered, vaporized parting liquid to the heating means in which theparting liquid is separated from the coal and the foreign material inthe gaseous state to vaporize the parting liquid associated with thecoal and foreign material; means for condensing vaporized parting liquidand for purging non-condensibles therefrom; and means for circulating tosaid condensing and purging means vaporized parting liquid in excess ofthat required to operate said heating means.
 40. Coal cleaning apparatusaccording to claim 39 together with means for diverting from the heatingmeans to the condensing and purging means vaporized parting liquid inexcess of that required to operate said heating means.
 41. Coal cleaningapparatus according to claim 40 together with means for automatically soregulating the diverting of the parting liquid vapor as to maintain aselected temperature in said heating means.
 42. Coal cleaning apparatusaccording to claim 39 together with a second source of heat independentof the vaporized parting liquid from which heat can be supplied to theheating means.
 43. Coal cleaning apparatus, comprising: a separator inwhich coal and foreign material can be separated by a parting liquid;means in which parting liquid can drain from coal and foreign materialdischarged from said separator; means for heating said coal and saidforeign material to vaporize and thereby separate additional partingliquid therefrom in the gaseous state; and means for recovering thevaporized parting liquid and converting it to liquid form, comprising: aheat exchange means; means for circulating vaporized parting liquid tosaid heat exchange means; and means for circulating a heat exchangefluid first to said heat exchange means to cool and thereby condense theparting liquid and to recover heat therefrom and then to the heatingmeans to vaporize the parting liquid associated with the coal and withthe foreign material.
 44. Coal cleaning apparatus according to claim 43together with a second heat exchange means to which the heat exchangefluid can be diverted before flowing to said heating means to removefrom said fluid heat in excess of that required to operate said heatingmeans.
 45. Coal cleaning apparatus according to claim 44 together withmeans for automatically so proportioning the flow of heat exchange fluidbetween the heating means and the second heat exchange means as tomaintain a selected temperature in said heating means.
 46. Coal cleaningapparatus according to claim 43 together with a second source of heatindependent of said heat exchange fluid from which heat can be suppliedto said heating means.
 47. Coal cleaning apparatus, comprising: asink-float separator in which coal and foreign matter can be separatedby gravity separation in a parting liquid; conditioner means upstream ofsaid separator for mixing parting liquid with the coal to be cleaned;means for transferring the coal and parting liquid from the conditionermeans to the separator; and means for changing the specific gravity ofthe parting liquid which comprises means for adding to the conditionermeans a liquid diluent which is miscible with the parting liquid and hasa different specific gravity than the parting liquid.
 48. Coal cleaningapparatus according to claim 47 together with means for recovering andstoring parting liquid and diluent removed from the separator inassociation with the coal and foreign material separated therein andmeans for circulating the parting liquid, diluent mixture to theconditioner means.
 49. Coal cleaning apparatus according to claim 48together with means for controlling the level of the liquid in theseparator.
 50. Coal cleaning apparatus, comprising: a separator in whichcoal and foreign matter can be separated by a parting liquid;conditioner means upstream of said separator for mixing parting liquidwith the coal to be cleaned; means for transferring the coal and partingliquid from the conditioner means to the separator; means for changingthe specific gravity of the parting liquid which comprises means foradding to the conditioner means a liquid diluent which is miscible withthe parting liquid and has a different specific gravity than the partingliquid; and means having a sensor responsive to the specific gravity ofthe parting liquid in the separator for automatically proportioning theflow of parting liquid and diluent to the conditioner means.
 51. Coalcleaning apparatus comprising: a separator in which coal and foreignmaterial can be separated by a parting liquid; means for varying theapparent temperature of the coal to be cleaned before it is introducedinto the separator to thereby control the specific gravity of theparting liquid in the separator; means for heating coal and foreignmaterial discharged from the separator to separate parting liquidtherefrom in the gaseous state; and a single heat source means forsupplying heat to said apparent temperature varying means and to themeans for heating the coal and the foreign material.
 52. Coal cleaningapparatus, comprising: a separator in which coal and foreign materialcan be separated by a mixture of a parting liquid and a liquid diluentwhich is miscible with said parting liquid; means for recovering liquiddischarged from the separator with the coal and foreign materialsseparated therein; and means for resolving the recovered liquid into theconstituents of the liquid mixture to thereby furnish parting liquid anddiluent which can be added to the liquid mixture in the separator tocontrol the specific gravity of said liquid mixture.
 53. Coal cleaningapparatus according to claim 52 wherein the means for resolving therecovered liquid into its original constituents includes means forseparating noncondensibles from said liquid, means for vaporizing theliquid, and a fractionating means for separating the diluent from theparting liquid.
 54. Coal cleaning apparatus according to claim 52together with separate storage means for said parting liquid, saiddiluent, and said parting liquid, diluent mixture and means responsiveto the level and specific gravity of the parting liquid, diluent mixturein the separator for so regulating the flow of parting liquid, diluent,and parting liquid, diluent mixture to said separator as to control thelevel and specific gravity of the parting liquid, diluent mixture in theseparator.
 55. Coal cleaning apparatus according to claim 54 whichincludes a conditioner means upstream from said separator and means bywhich parting liquid and diluent can be supplied to the conditionermeans and parting liquid, diluent mixture can be supplied to theseparator.
 56. A method of recovering coal from an association therewithof foreign matter, said method comprising the steps of: providing a bodyof a parting liquid; conveying the initial solids system containing thecoal to be beneficiated to and introducing it into the body of partingliquid, said parting liquid having a specific gravity intermediate thespecific gravities of the lighter coal and the heavier foreign material,whereby the coal will tend to rise toward the surface of the body ofparting liquid and the foreign material will tend to sink to the bottomthereof, thereby forming separate solids systems composed predominantlyof coal and of foreign material, respectively; and separately recoveringand conveying said separate solids systems from the body of partingliquid, said parting liquid comprising 1,2-difluoroethane or afluorochloro derivative of methane or ethane selected from the groupconsisting of 1-chloro-2,2,2-trifluoroethane,1,1-dichloro-2,2,2-trifluoroethane, dichlorofluoromethane,1-chloro-2-fluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane,1,1-dichloro-1,2,2,2-tetrafluoroethane, and trichlorofluoromethane, andat least one of said solids systems being conveyed to or from the bodyof parting liquid in a slurry comprised of the material composing thesystem and a fluorochloro derivative of methane or ethane selected fromthe aforesaid group thereof or 1,2-difluoroethane.
 57. A methodaccordingly to claim 56 in which all three of said solids systems areconveyed to and from the body of parting liquid in slurries comprised ofthe materials composing the respective systems and 1,2-difluoroethane ora fluorochloro derivative of methane or ethane as aforesaid.
 58. Amethod according to claim 56 in which the initial solids systemincluding the coal to be beneficiated is conveyed to the body of partingliquid in a slurry formed as aforesaid and including the step ofincorporating into said slurry prior to the introduction of the slurryinto the body of parting liquid a surface active agent of a characterand in an amount effective to cause water in the aforesaid initialsolids system to migrate toward that solids system in the lower part ofthe body of the parting liquid which includes the foreign material. 59.A method according to claim 56 in which the solids systems into whichthe initial solids system is separated in the body of parting liquid areconveyed therefrom in slurries formed with 1,2-difluoroethane or afluorochloro derivative of methane or ethane as aforesaid and includingthe step of recovering the fluorochloro derivative or 1,2-difluoroethanefrom at least one of said slurries at the location to which the slurryis conveyed.
 60. A method of beneficiating coal to remove foreign mattercomprised of surface water and unwanted, particulate solids therefrom inwhich the coal and associated foreign matter is introduced into a bodyof a parting liquid which is or contains a halogenated hydrocarbon andhas a specific gravity intermediate those of the coal and foreignmaterial so that the coal will rise toward the top of the body of liquidand the particulate solids in the foreign material will sink toward thebottom thereof, said parting liquid comprising 1,2-difluoroethane or afluorochloro derivative of methane or ethane selected from the groupconsisting of 1-chloro-2,2,2,-trifluoroethane,1,1-dichloro-2,2,2-trifluoroethane, dichlorofluoroethane,1-chloro-2-fluoroethane, 1,1,2-trichloro-1,2,2-trifluoroethane,1,1-dichloro-1,2,2,2-tetrafluoroethane, and trichlorofluoromethane, andthe coal being preconditioned with a mixture of from 0.03 to six poundsof surface active agent per ton of coal and a fluorochloro derivative asdescribed above or 1,2-difluoroethane and with or without agitationbefore said coal is introduced into the body of parting liquid wherebythe particulate solids will migrate toward the bottom of the bath ofparting liquid and carry with them surface water associated with thecoal being beneficiated, whereby said water will also become separatedfrom the coal.